Why Your Poly Bag Supplier Asks So Many Questions

You ask for a price on poly bags and the supplier answers with questions: What’s going in it? How heavy? Any sharp edges? Food contact? How will it be filled? If that feels like friction — you wanted a number, not an interview — here’s the reframe: those questions are free packaging engineering, and the suppliers who don’t ask them are the ones to worry about. Here’s what each question is actually solving.

“What’s going in the bag?”

This one question quietly decides the material. Food means FDA-compliant resin and the documentation behind it. Electronics might mean anti-static film. Metal parts that sit in storage might call for corrosion-inhibiting VCI bags. Retail product where looks matter leans toward high-clarity LDPE. The supplier isn’t being nosy — they’re routing you to the right film family before a dollar is spent.

“How much does it weigh?” and “Does it have edges?”

Together these set the thickness — the mil — which is most of your price. Weight stresses the film and the seals; corners and points concentrate force and punch through film that weight alone never would. A supplier who knows both numbers can often spec you thinner than you’d have guessed, saving money on every bag forever. One who doesn’t ask will either overbuild the bag (you overpay) or underbuild it (it fails). The full logic lives in our mil thickness guide.

“How will the bag be filled?”

A bag filled by hand on a table and a bag filled on an automated line are different products. Machine filling usually means wicket bags — stacked on a wire so the line can grab one after another — with the lip and hole spacing matched to your equipment. Hand filling might just mean an easy-open top. Answering this question prevents the expensive version of learning it: a pallet of bags your line can’t run.

“How does it get closed?”

Tape, heat sealer, twist tie, zip, fold-over — the closing method can change the bag’s length (you need material to close with), and sometimes the style. It’s a thirty-second question that prevents bags that are exactly product-sized and impossible to shut.

“Where does the bag go after that?”

Shipped loose in cartons? Stacked on pallets outdoors? Frozen? Displayed on a retail peg? Each destination pushes a spec: shipping abrasion favors tougher film, freezers favor materials that stay flexible when cold, retail pegs need hang holes, and bags over a certain size need a printed suffocation warning to satisfy many retailers. This is the question that catches requirements you didn’t know you had.

“How many, and is it recurring?”

Volume isn’t small talk — it’s economics. Machine setup costs the same for a short run or a long one, so quantity drives the per-bag price, and a recurring need can be scheduled as repeating production rather than quoted fresh each time. Honest numbers here get you honest pricing, including advice like “order these two items together and save the freight.”

The Pattern

Notice what just happened: six questions, and every one either saved you money, prevented a failure, or caught a hidden requirement. That consultation would cost real money from a packaging consultant — from a good supplier, it’s just how quoting works. This is also, quietly, the best reason to talk to a manufacturer directly: the person asking can see the machines that will run your job. (More on that chain in distributor vs. manufacturer.)

So next time, bring answers — our first-time buyer’s checklist covers all of them — and judge your suppliers by their questions. Want to experience the interview from the friendly side? Tell us what you’re packaging and we’ll start asking.

Somebody handed you the job of ordering poly bags, and you’ve never done it. Good news: every supplier on earth — distributor or factory — needs the same five answers from you. Gather them before you pick up the phone and you’ll sound like you’ve been buying film for years. Here’s the checklist.

1. What Goes in the Bag?

This is the question everything else hangs on, so answer it first and honestly. Not just the product name — the physical reality: How much does it weigh? Does it have corners, edges, or points? Is it food, or anything that touches food? Will the bag be the retail package a customer sees, or protection inside a box nobody sees? One sentence like “5-lb bags of machined steel fittings, boxed for shipping” or “single loaves of bread for a packing line” tells a good supplier half the spec.

2. What Size?

Bag sizes are written width × length — width across the opening, length top to bottom. Measure your product, then allow clearance: a product exactly 10″ wide will not slide into a 10″ bag. If the contents are boxy or bulky, you may need a gusset (a fold that lets the bag expand), which becomes a third number. Don’t agonize — get close and let the supplier fine-tune. The conventions and clearance rules are all in how to measure a poly bag, and our free Bag Builder draws the bag to scale as you type.

3. How Thick?

Thickness is measured in mil — thousandths of an inch — and it’s the biggest lever on both strength and price. The short version: around 1 mil for light protection, 1.5–2 mil for general use, 3–4 mil for heavy or sharp contents. Don’t guess high “to be safe” — thickness is resin, and you pay for it on every bag. Tell the supplier the weight and sharpness of your contents and let them recommend; the full logic is in what mil thickness does your bag need.

4. Open, Closed, or Printed?

Decide how the bag gets closed and whether anything is printed on it. Plain open-top bags (sealed by you with tape, heat, or a twist tie) are the default and the cheapest. Resealable tape, hang holes, vent holes, and wicketing for packing lines are all options with purposes. Printing — your logo, a suffocation warning, handling text — adds a one-time plate charge for the artwork plus a per-color cost. If you don’t need print on day one, you can always add it on a reorder.

5. How Many, How Often?

Custom-manufactured bags are made to order, so quantity shapes everything: machines take the same setup time whether the run is short or long, which is why minimums exist and why the price per bag drops as volume rises. Be ready to say roughly how many you need now and whether this is a one-time buy or a recurring need — a supplier can structure a repeating order very differently (and usually better) than a one-off. Always ask the lead time so your first order lands before you run out of whatever you’re using now.

Then Just Send It

That’s the whole checklist: contents, size, mil, closure/print, quantity. Put those five answers in an email and any competent supplier can quote you — and the questions they ask back will teach you the rest. (Those questions are a feature, not friction — we wrote a whole post on why.)

If you’d like your first order to come with patient explanations included, that’s genuinely our thing: we’re a family-owned factory in Los Angeles and we walk first-time buyers through this every week. Send us your five answers — rough is fine — and we’ll take it from there.

Here’s a quiet fact about the packaging industry: most businesses that buy poly bags have never spoken to the company that made them. They call a distributor, the distributor handles everything, and the actual factory stays invisible. That arrangement isn’t wrong — but it should be a choice, not a default you fell into because nobody explained the supply chain. So let’s explain it.

The Three Layers of the Bag Business

• Manufacturers make bags: they buy resin, extrude film, print it, and convert it into finished product. We’re one — our factory is in Los Angeles.
• Distributors buy from manufacturers (often many of them), warehouse the goods, and resell — usually alongside thousands of other products: boxes, tape, gloves, labels.
• Brokers own no inventory at all: they take your order and place it with a factory, adding a margin for the matchmaking.

Every layer adds real services — and a real markup. The question is simply whether you’re using the services you’re paying for.

What a Distributor Is Genuinely Good At

Fairness first, because distributors earn their place. If you need two cases of stock-size bags plus tape, boxes, and bubble wrap on one PO, a distributor is the right call — consolidation is their product. They stock standard sizes for immediate shipment, they let small buyers purchase below factory minimums, and one account covers a hundred different supplies. For small or mixed-basket buying, the markup buys you convenience that’s worth it.

What Changes When You Buy From the Factory

Different strengths live at the source:

• The middle margin comes out. On recurring volume — the same bags, ordered all year — a resale markup on every case adds up to real money.
• Custom is the native language. A distributor sells what’s on the shelf; a factory makes what you spec. Odd sizes, specific mil, your print, a particular resin blend — that’s just a production setup, not a special favor.
• Technical answers come from the people running the machines. Ask a factory “what mil do I need?” and you’re talking to someone who will actually extrude it — and who can often spec you down to a thinner, cheaper film, because they know what the material can do.
• Traceability is direct. For food packaging especially, buying from the certified facility means the lot documentation comes from the source, with no relay in between. (More on that in what “FDA food-grade” actually means.)
• Problems have an address. If a lot fails, you’re talking to the people who made it — a point we expanded in why domestic manufacturing matters.

The Honest Rule of Thumb

Buy from a distributor when you need variety in small amounts. Buy from a manufacturer when you need volume, customization, or accountability in one product. If poly bags are a line item you reorder every month — same size, same spec — you are the exact buyer the factory-direct model exists for, and you may be paying a convenience fee for convenience you’re not using.

How to Find Out What You’re Actually Paying

You don’t have to guess, and you don’t have to switch anything today. Pull your last invoice and note the spec — size, mil, material, print, quantity (if the invoice doesn’t say, our glossary will help you decode it). Then get a factory quote on the identical item and compare. Sometimes the distributor price holds up, and now you know. Often it doesn’t — and now you really know.

We’ll happily be your comparison point: send us the spec from your current invoice and we’ll quote it like-for-like from our Los Angeles factory. No pressure, no jargon — just the other number.

Your first poly bag quote can read like a foreign language: 2 mil LDPE lay flat, 10 x 15, 1,000/case. None of it is complicated — it’s just never explained. Here is every term you’re likely to meet on a quote or spec sheet, translated into plain English. Bookmark it; nobody should need a middleman just to read a quote.

Size and Thickness

• Width × Length — bag sizes are always written width first. Width is across the opening; length is top to bottom. A 10″ × 15″ bag opens along the 10″ side. (Full details, including the clearance you should allow: how to measure a poly bag.)
• Mil — the film’s thickness: one mil is one thousandth of an inch. Not a millimeter. Thickness is the biggest driver of both strength and price. (Some suppliers say “gauge” — 100 gauge = 1 mil.)
• Gusset — a fold tucked into the sides or bottom that lets the bag expand to hold boxy or bulky contents. Written as the middle number: 10 × 8 × 24 means an 8″ gusset.

Materials

• Resin — the raw plastic, bought as pellets and melted into film. Resin cost is the foundation of bag cost.
• LDPE — low-density polyethylene. The classic bag material: clear, glossy, flexible.
• LLDPE — linear low-density polyethylene. LDPE’s tougher sibling: stronger and more puncture-resistant per mil, slightly less clear. Most real-world film is a blend of the two — here’s when each one wins.
• Food grade / FDA compliant — the resin meets federal food-contact requirements. Worth asking about the documentation behind the claim, not just the phrase — we explain what to ask in what “FDA food-grade” actually means.

Bag Styles

• Lay flat — the basic open-top bag: two dimensions, no gusset. The default when nobody says otherwise. (Examples here.)
• Wicket bag — bags stacked on a wire (“wicket”) through holes in a lip above the opening, so a packing line can grab, fill, and tear off one at a time. Standard for bread, produce, and ice.
• Liner — a bag used inside something else: a box liner, drum liner, or trash liner. Sized to its container.
• Tubing — the film tube on a roll, not yet cut into bags. Buyers with unusual lengths seal and cut it themselves.

Printing and Extras

• Flexo / flexographic — the standard method for printing on film: flexible plates, fast presses, priced per color.
• Plate charge — a one-time cost to make the printing plates for your artwork. You pay it on the first order, not every order.
• Vent holes — small punched holes that let air escape so bags pack flat, or let produce breathe.
• Suffocation warning — the safety text printed on bags that could fit over a child’s head; required by many retailers and marketplaces.

Quantities and Money

• Case pack / case count — how many bags per box, e.g. 1,000/case. Pricing is usually quoted per thousand bags (“per M”).
• Minimum order quantity (MOQ) — the smallest run a supplier will produce. For custom manufacturing, minimums exist because setting up the machines costs the same whether the run is short or long.
• Lead time — how long until your order ships. Custom-manufactured bags are made to order, so always ask.
• lbs per 1,000 — the weight of film in a thousand bags (width × length × mil ÷ 15). Since bags are priced substantially by weight of plastic, this number is why the quote says what it says.

Now Read Your Quote Again

2 mil LDPE lay flat, 10 × 15, 1,000/case — a basic open-top bag, 10 inches across the opening, 15 deep, in clear low-density polyethylene two thousandths of an inch thick, boxed a thousand at a time. See? Not a foreign language — just vocabulary. If anything on a quote still doesn’t make sense, ask the supplier to explain it; any manufacturer worth buying from will. We’re happy to be the one you ask.

Most people who buy poly bags have never seen one made. That’s a disadvantage: when the process is a mystery, every spec feels like something you need a middleman to handle. So here’s the whole journey — from a pellet of resin to a finished bag in a box — exactly as it happens on our floor in Los Angeles.

Step 1: It Arrives as Pellets

Polyethylene resin shows up at the factory as pellets the size of lentils, by the truckload. Different resins have different personalities — some are clearer, some are tougher, some are certified for food contact — and a real factory keeps several on hand. Most film is actually a blend of resins, mixed for the job: a bit more of one for strength, more of another for clarity. The blend is the first decision in every order, made before any machine turns on.

Step 2: The Blown-Film Tower

This is the part worth seeing. The pellets are fed into an extruder — essentially a heated barrel with a screw inside — which melts them into thick liquid plastic. The melt is pushed up through a ring-shaped die, and air inflates it into a bubble, often two or three stories tall. Picture blowing a soap bubble that never pops: the plastic stretches thin as it rises, cools in the air, and is drawn up the tower as a continuous tube of film.

At the top, rollers flatten the bubble and wind it up. Two numbers are locked in right here, at the die: the film’s width (set by the bubble’s size) and its thickness, measured in mil — thousandths of an inch. Get those right and everything downstream is straightforward; this is why it matters whether your supplier controls the extrusion or buys film from someone else.

Step 3: Printing

If the bag carries a logo, a suffocation warning, or handling text, the roll goes to a flexographic press — flexo, in shop language. Flexo is modern rubber-stamping at industrial speed: a flexible printing plate picks up ink and rolls it onto the moving film, one station per color. It’s the workhorse printing method for packaging because it’s fast, durable, and economical at volume. Unprinted bags skip this step entirely.

Step 4: Converting — Where Film Becomes Bags

“Converting” is the industry’s word for turning rolls of film into finished product. A bag machine pulls the film tube through, and for a basic bag does just two things, hundreds of times a minute: heat-seals a line across the tube (that’s the bag bottom) and cuts just above it (that’s the next bag’s opening). Because blown film starts life as a tube, the sides of a simple bag need no seams at all.

Variations happen here too: folding tucks into the sides to make gusseted bags that open into a squared shape, punching vent holes, or adding the lip and holes that let wicket bags hang on a wire for fast packing lines. Then bags are counted, boxed, and labeled — each case traceable back to the film roll and resin lot it came from.

Why “Under One Roof” Keeps Coming Up

You’ll see manufacturers (including us) make a point of doing extrusion, printing, and converting in one facility. Now you can see why it matters: the bag’s strength is decided at the extruder, its look at the press, its size at the bag machine. When those are three different companies, a problem becomes a finger-pointing exercise. When they’re one floor, it’s a short walk — and the lot traceability that food-safety audits demand stays intact from pellet to box.

The Takeaway for Buyers

A poly bag is resin, blown into film at a set width and mil, optionally printed, then sealed and cut. That’s the entire secret. Which means when a supplier asks you about dimensions, thickness, print, and quantity, they’re just asking which settings to run the machines at — and you can answer those questions directly to a factory as easily as to a distributor. New to the vocabulary? Keep our quote glossary open while you read your next quote, or tell us what you’re packaging and we’ll spec it with you from our floor at 1800 E. 50th Street.

If your job suddenly includes ordering “poly bags” and you’re not entirely sure what plastic even is — you’re in good company. Most people who buy packaging were never taught the basics. This is the explanation we wish every new buyer got on day one, with no chemistry degree required.

Plastic Is Not One Material

“Plastic” is like “metal.” Nobody would confuse a steel beam with a gold ring, but both are metal. The same is true of plastic: the water bottle, the milk jug, the PVC pipe, and the sandwich bag are all plastic — and they’re all different materials with different names, properties, and prices. When a supplier asks what plastic you need, “just plastic” is like answering “just metal.”

The big families you’ll hear about in packaging:

• Polyethylene (PE) — soft, flexible, slightly waxy feel. This is the plastic of bags, liners, and stretchy film. It’s what we make.
• Polypropylene (PP) — crisper and crinklier. The clear, glossy bags on greeting cards and the crinkly snack-food wrappers.
• PET (polyester) — rigid and glass-clear. Water and soda bottles.
• PVC, polystyrene, and others — pipes, foam cups, clamshells. Different jobs entirely.

Polyethylene: The Plastic of Bags

Nearly every flexible bag in your life — grocery bags, bread bags, trash liners, the bag inside a cereal box — is polyethylene. It earned that job because it’s flexible without plasticizers, it seals to itself with simple heat, it shrugs off water and most chemicals, and food-contact grades are well established with the FDA.

Even within polyethylene there are branches. The two that matter for bags are LDPE (low-density polyethylene — clearer and crisper) and LLDPE (linear low-density — stronger and stretchier). You don’t need to memorize them; just know the choice exists, and that it changes how a bag performs. When you’re ready for that level of detail, we wrote a full comparison in LDPE vs LLDPE.

What “Resin” Means

You’ll hear bag people say “resin” constantly. Resin is simply the raw material: polyethylene fresh from the chemical plant, shipped as small pellets about the size of lentils. A bag factory buys resin by the railcar or truckload, melts it down, and forms it into film. When someone says “resin prices moved,” that’s the packaging equivalent of a baker saying flour prices moved — it flows straight into the price of the finished bag.

Film Before Bag

Here’s the part most buyers never see: bags aren’t molded like bottles. Polyethylene is first turned into film — a continuous, thin sheet of plastic, made by melting resin and blowing it into a huge bubble that’s flattened and wound onto rolls. Bags are then cut and heat-sealed from that film. The film’s thickness is measured in mil — one thousandth of an inch — and that single number drives most of a bag’s strength and most of its cost. (That’s a big enough topic that we gave it its own guide.)

Why This Matters to You as a Buyer

Because once you know these four words — polyethylene, resin, film, mil — the mystery is mostly gone. A poly bag is polyethylene resin, melted into film of a certain mil, cut and sealed to a size. Every quote you’ll ever read is some arrangement of those facts. And that means you don’t have to treat packaging as a black box that only a big distributor can navigate for you: you can describe what you need to anyone, including the factory that actually makes it.

Keep Going

Next in this series: how a poly bag is actually made — a walk through the factory from pellet to sealed bag. Or if you have a quote sitting in your inbox right now and need the vocabulary decoded, jump to our plain-English glossary. And if you’d rather just ask a human: we’re a family-owned manufacturer in Los Angeles, and explaining this stuff is part of the job. Send us what you’re trying to package — no jargon required on your end.

Poly bags are a commodity — until something goes wrong. A late container, a failed lot with no paper trail, a spec change that takes three time zones and two weeks to communicate. Where your bags are made doesn’t matter on the good days. It matters enormously on the bad ones. Here’s the case for buying film manufactured domestically — specifically, from our floor in Los Angeles.

Traceability You Can Actually Audit

When film is extruded, printed, and converted in one domestic facility, every finished lot traces back to the resin lot it was made from — and you can verify that, in person if you want. That’s not a luxury. For food packaging it’s the backbone of a recall plan, and for QA teams it’s the difference between a certificate you can check and a certificate you have to take on faith. It’s also the foundation under food-safety certifications and third-party audits, which we’ve written about in what “FDA food-grade” actually means.

The Supply Chain You Don’t Have to Think About

Imported packaging means ocean transit, port schedules, customs, and tariff changes — none of which you control, all of which can idle a packing line. Domestic manufacturing doesn’t make supply chains magically perfect, but it removes the longest and least predictable links. When your bag supplier and your packing line are on the same continent, a problem is a phone call and a truck, not a vessel booking.

Freight Math Favors Proximity

Poly bags are bulky for their value, which makes freight a meaningful slice of landed cost. From Los Angeles, the entire West Coast is short-haul territory: California next-day to a few days by ground, and the Pacific Northwest, Nevada, and Arizona well within economical LTL range. For West Coast buyers, a local manufacturer isn’t just convenient — it’s structurally cheaper to ship from. (And for buyers further out, we publish honest transit expectations rather than promises — see our service area pages.)

Changes Happen at Conversation Speed

Packaging specs aren’t static: a new product size, a print revision, a thickness change after a line trial. With an overseas supplier, each iteration rides the same multi-week pipeline as the order itself. With a manufacturer in your time zone, a spec discussion happens the same day, with the people who will actually run the job — because the extrusion, printing, and converting all happen under one roof in Vernon, not at a subcontractor you’ll never speak to.

Accountability Has an Address

We’re a family-owned manufacturer, and our plant is at 1800 E. 50th Street in Los Angeles. Customers tour it. Auditors inspect it. If a lot ever has a problem, the people responsible for fixing it are the people who made it — not a trading company between you and an anonymous factory. That accountability is ultimately what “domestic manufacturing” buys: not a flag on a label, but a shorter distance between a problem and the person who can solve it.

Put It to the Test

The next time you re-quote your packaging, get a domestic number alongside the import price and compare landed cost — freight, lead-time risk, and the cost of carrying extra safety stock against a long pipeline. Request a quote and we’ll give you the Los Angeles number to compare.

Every poly bag quote starts with three numbers: width, length, and mil. The first two are decided by your product. The third one — thickness — is where buyers most often overspend or underspec. Here’s how to land on the right mil without guessing.

What a Mil Actually Is

A mil is one thousandth of an inch (0.001″). It is not a millimeter — a millimeter is nearly 40 mil. You may also see film listed in “gauge” (100 gauge = 1 mil); we spec everything in mil. For reference, a typical grocery sack runs well under 1 mil, while a heavy contractor-style liner can run 3 mil or more.

The Two Questions That Decide Thickness

Forget charts for a second. Film thickness answers two questions:

1. How much does the contents weigh? More weight means more stress on the film and the seals.
2. Does the contents have edges? Corners, threads, burrs, and points concentrate force. A 5-lb machined part is harder on a bag than 5 lbs of flour.

Weight pushes you up in mil gradually. Edges push you up fast.

General Starting Points

• 1 mil — light-duty protection: dust covers, garment and literature bags, light produce. Film protects against contact and contamination, not load.
• 1.5–2 mil — the general-purpose range: most lay flat bags, food packaging, parts without sharp edges, shipping-carton liners.
• 3 mil — heavier contents and moderate abuse: hardware, bulk food, packaged ice, liners that get dragged and lifted.
• 4 mil — sharp or heavy industrial contents: fasteners, castings, demolition debris, rock and gravel.
• 6 mil and up — extreme duty, where film failure is expensive enough to justify the resin.

Treat these as starting points, not answers. The same 2-mil film that’s generous for packaged bakery goods is undersized for bolts.

Thickness Is Most of Your Price

Poly bags are priced substantially by weight of film, and weight scales directly with mil: a 4-mil bag uses twice the resin of a 2-mil bag of the same size. The formula is simple — width × length × mil ÷ 15 = lbs per 1,000 bags — and it means every unnecessary mil is paid for on every bag, forever. This is why “just make it thick to be safe” is the most expensive sentence in packaging.

The reverse also holds: material choice can buy strength without thickness. LLDPE-rich blends resist puncture better per mil than standard LDPE, which often allows a thinner, cheaper film at the same real-world performance — we covered the tradeoffs in LDPE vs LLDPE.

When In Doubt, Sample It

The honest answer to “what mil do I need?” is sometimes “let’s test it.” Film behavior with your actual product — your weights, your edges, your handling — settles debates that charts can’t. Our Bag Builder calculates film weight live as you adjust mil, so you can see the cost impact of each option before you ask for it. Then request a quote and tell us what’s going in the bag — we’ll tell you if the mil you picked is more than you need.

Both are polyethylene. Both make clear, flexible film. Both show up on spec sheets for the same kinds of bags. But LDPE and LLDPE behave differently enough that choosing the wrong one means paying for properties you don’t need — or losing ones you do.

The Difference Is Molecular Shape

LDPE (low-density polyethylene) is made under high pressure, which produces long, randomly branched polymer chains. Those branches keep the chains from packing tightly — hence “low density” — and give the film its signature feel: glossy, clear, and relatively stiff for its weight.

LLDPE (linear low-density polyethylene) is made with catalysts that build linear chains with short, regular branches. The chains align and grip each other better under stress, which translates directly into strength: higher tensile strength, better puncture resistance, and more stretch before failure than LDPE at the same thickness.

What That Means in a Bag

In practice: LDPE is the pick when presentation matters — retail packaging, display bags, anything where the customer sees the product through the film. It also runs beautifully through printing. LLDPE earns its keep where the bag takes abuse: liners loaded with heavy or irregular contents, box liners under industrial fill, bags carrying parts with corners and edges.

The Downgauging Advantage

Because LLDPE is stronger per mil, it often lets you run a thinner film at the same performance — a 1.5-mil LLDPE liner can replace a 2-mil LDPE liner in many duties. Thinner film means fewer pounds of resin per thousand bags, and since poly bags are priced by weight, that’s a real cost lever on high-volume items.

You Usually Don’t Have to Choose

Most film that comes off a modern blown-film line is neither pure LDPE nor pure LLDPE — it’s a blend, tuned for the job. A retail bag might blend in LLDPE for tear strength while keeping LDPE’s clarity; an industrial liner might run LLDPE-rich for puncture resistance. Because we run our own extrusion in-house, the blend is a specification we control per order, not a stock item we resell.

Both Can Be Food-Grade

FDA food-contact compliance is about the resin meeting federal requirements, not about which polyethylene family it belongs to. LDPE and LLDPE food-compliant resins are both available — what matters is the documentation and the facility behind them, which we’ve covered in detail in our guide to what “FDA food-grade” actually means.

The Short Version

Clarity, crispness, printability — lean LDPE. Strength, puncture resistance, downgauging economics — lean LLDPE. Carrying something heavy, sharp, or expensive — tell us what it is and we’ll spec the blend. Request a quote with your product details and we’ll recommend the right film, not just the right size.

Order the wrong size and a poly bag either won’t fit the product or wastes film on every unit. Yet most sizing mistakes trace back to the same thing: bag dimensions follow conventions that nobody explains. Here’s how poly bags are actually measured — and how to spec yours right the first time.

Width × Length: The Base Convention

Flat poly bags are always listed width first, then length. Width is the distance across the bag opening, seam to seam. Length runs from the opening down to the bottom of the bag. A 10″ × 15″ bag opens along the 10″ side and is 15″ deep.

Two details trip people up:

• Measurements are outside dimensions. Side seams and the bottom seal each take up a small amount of the stated size, so the usable interior is slightly smaller. If your product measures exactly 10″ wide, it will not slide into a 10″ bag — allow clearance.
• Allow for product thickness. A flat measurement doesn’t account for depth. A common rule: add the product’s thickness to the bag width, and half the thickness plus closing allowance to the length.

Gussets: The Third Number

A gusseted bag adds a folded expansion panel, written as the middle number: 10″ × 8″ × 24″ means 10″ wide with an 8″ gusset. There are two kinds:

• Side gussets fold into the sides, letting the bag open into a squared shape for boxes, bulk product, and container liners. When fully opened, the bag face measures the width plus the full gusset.
• Bottom gussets fold into the bottom, letting the bag stand or wrap under a product. A bottom gusset is measured folded — the bag “opens to” a longer usable length.

One physical constraint worth knowing: a gusset can never be deeper than the bag is wide, because the fold has to fit inside the film tube it’s made from.

Mil: The Thickness Number

Poly bag thickness is measured in mil — one thousandth of an inch. (Some suppliers list “gauge”: 100 gauge equals 1 mil. We spec everything in mil.) A 1-mil bag handles light-duty protection; 2 mil is a common all-purpose weight; 3–4 mil carries heavier or more abrasive contents. Thickness is a strength decision, not a size decision — and it’s the biggest driver of bag cost, because thicker film means more resin per bag.

Wicket Bags: Add the Lip

Bags that run on automated lines — bread, produce, ice — hang on a metal wicket through a lip: an extension above the bag opening, typically a couple of inches, where the wicket holes punch through. A wicket bag spec adds lip and wicket-hole spacing to the usual width, length, gusset, and mil.

Estimating Bag Weight

Film is sold by the pound, so weight is how the economics work. The industry formula for flat bags:

lbs per 1,000 bags = width × length × mil ÷ 15

Gussets and lips add their share of film — a side gusset adds its full depth to the width; a bottom gusset adds half its depth to the length. This is exactly the math our online builders run live as you change dimensions.

Skip the Math — Use the Builders

We built free tools that draw your bag to scale and calculate weights as you type: the Bag Builder for flat and gusseted bags, the Wicket Bag Builder for wicketed styles, and the Tubing Builder for poly tubing by the roll. Spec it, see it drawn, and send it to us as a quote request in one step.

Still unsure what size fits your product? Send us the product dimensions — sizing bags to products is what we do all day.