What is a Poly Mailer? Learn More About the Many Benefits and Uses.

Shippo Snippets:

• A poly mailer is a lightweight, water-resistant polyethylene shipping bag that replaces a box for soft goods like apparel. Small (7.5×10.5"), medium (10×13"), and large (14.5×19") cover most orders.
• Ship one via USPS Ground Advantage for around $6 to $10 depending on size and weight (Shippo commercial rates, San Francisco to New York, July 2026).
• UPS and FedEx both charge an Additional Handling Surcharge on poly mailers that exceed specific dimensions. Standard sizes stay under those thresholds.
• Poly mailers aren't curbside recyclable. Most need a store drop-off program instead.

A poly mailer is a lightweight, moisture-resistant polyethylene bag that ships soft goods in place of a box, cutting both postage cost and storage space compared to corrugated cardboard. Below: what poly mailers are made of, which size fits your product, real shipping rates, and the carrier rules that decide when a mailer is the right call and when a box still wins.

In this article

• What Are Poly Mailers Made Of?
• Poly Mailer Sizes and Weight Limits
• Poly Mailer Varieties
• How Much Do Poly Mailers Cost to Ship?
• Carrier Rules and Restrictions for Poly Mailers
• Poly Mailers vs. Boxes: Which Should You Use?
• Are Poly Mailers Recyclable?
• Can Poly Mailers Be Customized?
• What's New in 2026: USPS Cubic Pricing for Poly Mailers
• FAQ: Poly Mailers

What Are Poly Mailers Made Of?

Poly mailers are made of polyethylene, a light, synthetic resin that's the most widely used plastic in the world. It's the same material behind shopping bags, food wrap, and detergent bottles. Most standard mailers use low-density polyethylene (LDPE) film, which gives them their stretch, tear resistance, and water resistance without adding weight to the package.

Poly Mailer Sizes and Weight Limits

A poly mailer doesn't carry its own official weight limit. The limit that applies is whichever shipping service prints the label, not the bag itself. USPS Ground Advantage, the most common service for mailers, caps out at 70 lb and 130" in combined length and girth, far more than any poly mailer realistically needs to carry. Size is the bigger constraint in practice: pick a mailer that fits the product snugly, since an overfilled or underfilled bag causes more shipping problems than a slightly heavy one.

Here's a general guide by size:

Poly Mailer Varieties

There are several types of poly mailers to choose from, depending on what you're shipping:

Layflat Poly Mailers

Layflat poly mailer bags are the industry standard, the flat plastic bag you've probably received from most online orders. They hold a wide array of items, work well for goods that don't need much cushioning, and seal with a self-adhesive strip.

Clear View Poly Mailers

Clear view poly mailers are a solid choice for shipping print materials like catalogs, brochures, and magazines. They're transparent on one side with an opaque backside for postage and labels.

Bubble-Lined Poly Mailers

For fragile goods that don't need a fully packaged box, bubble-lined poly mailers offer extra cushioning at a lower cost than a padded box. They're usually self-sealable and a good fit for small, delicate items.

Expansion Poly Mailers

Expansion poly mailers have an expandable, durable seam along the side, making them easier to fill for bulkier items like jackets, sweatshirts, books, or binders.

Returnable Poly Mailers

Returnable poly mailers plan ahead for the returns that come with selling online. They have two self-seal adhesive closures, so a customer can reseal the same bag to send an order back to your receiving address.

Recycled Poly Mailers

100% recycled poly mailer bags are made from a mix of post-industrial and post-consumer materials, with a lower carbon footprint than mailers made from new plastic.

How Much Do Poly Mailers Cost to Ship?

Poly mailers keep dimensional (DIM) weight low. That's most of why they cost less to ship than a box carrying the same item: light, thin packages qualify for cheaper service tiers that a rigid box often can't reach. Here's what that looks like using two of the sizes from the table above:

Rates are Shippo commercial rates pulled July 15, 2026, for a shipment from San Francisco, CA (94117) to New York, NY (10001). Actual rates vary by your account's negotiated pricing, origin and destination, and carrier fuel surcharges. Use Shippo's rate calculator to check current pricing for your own shipment.

The cheapest option shifts by size and weight. That holds true for comparing USPS, UPS, and FedEx rates generally, so it's worth checking live rates across carriers for each shipment rather than defaulting to one.

Carrier Rules and Restrictions for Poly Mailers

Poly mailers ship fine with all three major U.S. carriers, but each has rules that affect eligibility or cost once a mailer gets larger or heavier than the smallest sizes.

USPS doesn't require a minimum thickness or rigidity for parcels shipped as Ground Advantage packages, so a standard poly mailer qualifies without special handling. Nonstandard-length fees do apply once a package runs long, whether it's a mailer or a box: $4.50 for 22 to 30 inches, $10.00 for over 30 inches, and $21.00 if it exceeds 2 cubic feet, per USPS Notice 123.

UPS and FedEx handle oversized soft-sided packaging differently than USPS. Both apply an Additional Handling surcharge once a poly bag or bubble mailer exceeds certain dimensions:

A standard large poly mailer (14.5×19") stays under both thresholds, but an overstuffed one won't. The height trigger catches people off guard the most: FedEx's 5" limit means a lumpy, unevenly packed mailer can cross it without looking obviously oversized. Standard poly mailer sizes rarely trip these surcharges, but stuffing a mailer past its intended capacity to avoid a box can end up costing more than the box would have.

Poly Mailers vs. Boxes: Which Should You Use?

Poly mailers win on cost and storage for the right products. A stack of poly mailers takes up far less space than the same number of collapsed cardboard boxes, and a mailer skips the assembly a corrugated box requires. They're also weather-resistant and hard to tear, holding up well in transit despite weighing much less than a box.

A box is still the better call in a few situations. Fragile or breakable contents need a bubble-lined mailer or a padded box, not a standard poly mailer. Shipping several items at once, unless they're soft apparel, usually packs and travels better in a box with void fill. And a product that doesn't sit flat in any standard mailer size creates gaps or flat spots that carrier scanning equipment can misread, leading to sorting errors, delays, or a Return to Sender; a padded box like the ones used for shipping books is worth the extra cost in that case.

Are Poly Mailers Recyclable?

Most poly mailers are made from LDPE or HDPE plastic film, and most curbside recycling programs don't accept them because the film can jam sorting equipment at material recovery facilities. Poly mailers instead need to go through a store drop-off program, the same bins many grocery and retail stores use for plastic shopping bags, per How2Recycle's guidance. To qualify, the mailer needs to be clean, dry, and free of paper shipping labels before it goes in the bin. 100% recycled poly mailers (see varieties above) cut the footprint of the packaging itself, though the disposal path stays the same either way.

Can Poly Mailers Be Customized?

According to a Paper and Packaging Board survey, 72% of consumers say packaging design influences their purchasing decisions, giving merchants a real opening to make an impression with something as simple as a mailer.

Poly mailers are easy to customize and can help reinforce brand loyalty. A few ways to do it:

• Choose a size that fits your shipment
• Change the background color to match your brand
• Add a logo or a catchy design
• Feature compelling or witty text that engages customers

What's New in 2026: USPS Cubic Pricing for Poly Mailers

Effective July 12, 2026, USPS restructured Ground Advantage Cubic pricing for softpack shipments, which includes poly mailers and padded envelopes. The tier count dropped from ten to five, and the measurement method now aligns with Priority Mail Cubic, pricing off combined length plus width instead of the old tier structure. High-volume shippers who qualify for Cubic pricing should run a fresh rate check even if nothing else about their packaging changed. See Shippo's guide to USPS Cubic pricing for how the tiers work and whether your shipment volume qualifies.

FAQ: Poly Mailers

What size poly mailer do I need? Match the mailer to the product for a snug fit; that ships more reliably than an oversized bag with excess air inside. Use the size table above as a starting point, and size up only if the product doesn't fit without folding awkwardly.

Can I ship a poly mailer with UPS or FedEx? Yes. Both carriers accept poly mailers, though each charges an Additional Handling surcharge once a soft-sided package exceeds the thresholds in the carrier rules section above.

What mil thickness should I use? 2.5 mil is the common standard for apparel and general soft goods. Heavier or sharp-edged items may need a thicker mailer to avoid punctures in transit.

Shippo Can Help

Compare live rates across 40+ carriers, including USPS, UPS, and FedEx, for your next poly mailer shipment with Shippo.