A poly mailer often costs less to ship than a box carrying the exact same shirt. Carriers price soft, flexible packaging differently than rigid boxes, and that gap adds up fast across a full shipping season.
Poly mailers are not a fit for everything though. Here is every standard size, what belongs in each one, and when a box is still the better call.
Standard poly mailer sizes
| Size | Typical contents |
|---|---|
| 6×9 in | Jewelry, phone cases, small accessories |
| 9×12 in | Documents, thin apparel, magazines |
| 10×13 in | T shirts, books, small apparel |
| 12×15.5 in | Sweaters, small electronics, boxed items |
| 14.5×19 in | Jackets, multiple clothing items |
| 19×24 in | Bulk apparel, oversized soft goods |
A simple sizing rule works for most items. Add the product width to twice the product thickness, then add 1 to 2 inches for sealing room.
When poly mailers work well
Soft, bendable items are the ideal fit. Clothing, fabric goods, and anything that will not crush or bend out of shape ships safely in a poly mailer.
Poly mailers also weigh far less than a box, which matters on carriers that price by actual weight rather than cubic size. That weight savings is where much of the cost advantage comes from.
When a box is still the better choice
Rigid or semi rigid items are the real risk zone. Real sellers have flagged shoes specifically as a problem, since a poly mailer offers no structure and shoes can bend, crease, or lose shape in transit.
The general rule from experienced sellers holds up well: if an item could bend, get crushed, or lose its shape, put it in a box instead. Our full guide to shipping boxes covers sizing for anything that needs real structure.
Padded poly mailers
Bubble lined poly mailers add a layer of cushioning for items that need light protection but not full rigid packaging. They cost more than plain poly mailers but less than a box plus separate bubble wrap.
USPS also sells its own padded flat rate envelope for Priority Mail specifically, distinct from a generic bubble mailer. Our full flat rate pricing guide covers that fixed price option.
Mailing a poly mailer through USPS
A poly mailer’s plastic exterior can trigger a nonmachinable surcharge if it ships at letter rates instead of package rates. Our full guide to stamps on bubble and padded mailers covers exactly how much postage a mailer actually needs.
Getting the postage right the first time avoids a returned package and a second trip to the mailbox. Our tool for checking the exact postage owed can confirm the amount before you seal anything.
Where to buy poly mailers
Office supply and shipping specialty stores carry small quantities for occasional shippers. Bulk suppliers offer a noticeably lower cost per mailer for anyone shipping clothing or soft goods regularly.
Our full comparison of the best poly mailers for clothing covers specific brand picks by size and price.
Frequently asked questions
What size poly mailer should I use?
Add the item width to twice its thickness, then add 1 to 2 inches for sealing room. Most clothing items fit a 10×13 or 12×15.5 inch mailer.
Are poly mailers cheaper to ship than boxes?
Often, yes, since they weigh far less and some carriers price by actual weight. The savings depend on the specific carrier and service used.
Can I ship shoes in a poly mailer?
It is risky, since a poly mailer offers no structure and shoes can bend or lose shape. A box is the safer choice for anything rigid.
Do poly mailers need extra postage?
Sometimes, since the plastic exterior can trigger a nonmachinable surcharge at letter rates. Package rate postage usually avoids that issue entirely.
Are poly mailers waterproof?
Yes, generally, since the plastic material resists water better than a cardboard box. Seams and the seal strip are the weak points if moisture is a real concern.
The bottom line
Poly mailers save weight, space, and often money for anything soft enough to survive without structure. Anything that could bend, crush, or lose shape still belongs in a box.
Match the size to the item using the width plus twice the thickness rule, and check postage with our stamp calculator before you ship.
