How to Choose the Right Poly Bag Thickness (Mil) for Your Product

What “mil” means

In the United States, poly bag thickness is measured in mils. One mil is one thousandth of an inch (0.001"). It has nothing to do with millimeters: a millimeter is about 39 times thicker than a mil.

You may also see thickness written as gauge. In poly film, 100 gauge equals 1 mil, so a 150 gauge film is 1.5 mil. Outside the US, film is often measured in microns, and 1 mil is about 25 microns.

One more thing to know: thickness usually refers to a single wall of the bag. A 2 mil bag has a front panel and a back panel that are each 2 mil thick.

Thicker is not always stronger

It is natural to assume a thicker bag is a better bag, but thickness is only one part of strength. The type of film matters just as much.

• Polyethylene (PE) is soft and flexible and stretches before it tears. It is a common choice for bread, produce, frozen food and general packaging.
• Polypropylene (PP) is stiffer and clearer. It shows the product off well, but it behaves differently from PE under impact and in the cold, so the same thickness does not perform the same way.
• Different grades and blends of the same film also differ, which is why two bags of the same mil can feel and perform very differently.

That is why the best answer to “how thick should my bag be?” starts with the product and how the bag will be used, and then lands on a film and a thickness together.

Questions that decide the thickness

Before you pick a number, think through these questions:

• How heavy is the product in each bag? Heavier fills put more stress on the seals and the film.
• Does it have sharp corners, edges or points? Hardware, frozen pieces and some baked goods can puncture thin film.
• Where is it stored? Freezers make some films more brittle, and products that sit on a shelf for weeks need a bag that holds up to handling.
• How is it filled? Automatic and semi-automatic baggers need film that runs consistently and opens cleanly.
• How does it travel? A bag that ships inside a box has an easier life than one that goes straight into a delivery van or a mailbox.
• Is the customer meant to see the product? Thinner, clearer film can show off the product better.

A general guide by use

Every product is different, so treat these as starting points to discuss with your supplier, not rules.

Lighter products. Bread and rolls, fresh produce, small soft goods and inner bags that go inside a box usually do well in the thinner range of film. The bag mainly needs to protect the product and look good, and thinner film keeps it light and clear.

Everyday retail and food. Most printed retail bags, frozen vegetables, snacks and similar products sit in the middle range. The bag has to survive shipping, shelving and handling by customers, and it often carries full branding.

Heavy or sharp products. Heavier fills, bulky items, hardware and anything with points or edges call for thicker film, a stronger film type, or a different bag style such as a bottom gusset that spreads the weight.

Shipping. Bags that travel on their own, such as poly mailers, need to resist tears and punctures from sorting and handling, so they are usually built heavier than bags that ship inside a box.

Size and style matter too

Thickness and bag size work together. A large bag holding a heavy product puts more strain on the film than a small bag holding the same weight, because the load is spread over a bigger panel and longer seals.

The bag style can do some of the work for you. Bottom gusset bags give heavier or bulkier products a base to sit on, and wicketed poly bags are made to load cleanly on bagging lines. Sometimes the right fix is a different style, not a thicker bag.

Features matter as well. A zipper adds weight near the top of the bag, and features like Anti-Fog, UV protection, Cold Seal or Anti-Static are chosen for how the product is stored and shown, not for strength.

Printing and thickness

Thickness has little effect on how good your printing looks. We print poly bags with flexographic printing in up to 8 colors, on thin and thick films alike. What changes is the feel in a customer's hand: a thicker bag feels sturdier, and a thinner one feels lighter and shows more of the product.

The cost of getting it wrong

Choosing too thin a film shows up as split seams, punctures, product damage and complaints. Choosing too thick a film is quieter, but you pay for extra film on every bag you order, and the bags take more room in storage.

The best way to find the right thickness is to test. Fill a few sample bags with your real product, handle them the way your customers and staff will, and see how they hold up. A good supplier will help you narrow the choice before you test.

Get help choosing

Metropolitan Packaging has made custom printed poly bags in Brooklyn, New York for more than 60 years, with printing and bag making done in house. We work with PE and PP films, including FDA-compliant materials for food.

Tell us what you are packing, how much goes in each bag and how it is filled and shipped, and we will recommend a film and thickness. Our minimum order is 10,000 for most bags, and 5,000 for stand-up, flat-bottom box and quad-seal pouches. Request a quote, call 1-800-642-0165 or email Sales@metropack.com.