Identical shirts, identical ZIPs, one quote day. Only the packaging changed, and so did every price.
The bag: 13 × 10 × 2 in at 0.9 lb, quoted 2026-07-27
| Carrier | Service | Price | Quoted transit |
|---|---|---|---|
| USPS | Ground Advantage | $9.91 | 6-7 business days |
| FedEx | Ground Economy | $10.06 | 4-5 business days |
| UPS | Ground | $10.31 | 3-4 business days |
| UPS | 3 Day Select | $15.13 | 3-4 business days |
| UPS | 2nd Day Air | $16.58 | 2-3 business days |
The box: 13.8 × 9.8 × 3.9 in at 1.3 lb, same day, same shirts
| Carrier | Service | Price | Quoted transit |
|---|---|---|---|
| UPS | Ground Saver | $10.52 | 4 business days |
| UPS | Ground | $11.07 | 3-4 business days |
| USPS | Ground Advantage | $11.17 | 6-7 business days |
| FedEx | Ground Economy | $11.78 | 4-5 business days |
| UPS | 3 Day Select | $16.37 | 3-4 business days |
Compare the tables service by service and the bag wins each matchup, by around a dollar on the ground tiers. Nothing clever happened. The mailer weighed less and displaced less space, pricing followed, and across a store’s monthly volume that stack of small differences turns into real margin.
Why thin packages dodge dimensional weight
USPS applies dimensional pricing to parcels bigger than one cubic foot, 1,728 cubic inches, billing the greater of scale weight or length × width × height divided by 139, per pe.usps.com/text/dmm300/123.htm, checked 2026-07-27.
A filled 10 × 13 mailer occupies a small fraction of that threshold, so the rule never reaches it. Boxes flirt with the line far sooner, above all the half-empty ones, and the fatter the package the more the divisor has to work with. Staying flat keeps a package out of volume pricing entirely, at zero cost.
Using the bag well
Right cargo for a bag
Clothing, bedding, plush toys and anything else that shrugs off a squeeze belongs in a poly mailer. If the item dents, snaps or scuffs, it needs walls.
Seal it like weather exists
Use the adhesive strip end to end and tape the corners. For fabric with resale value, an inner clear bag keeps rain and depot grime off the goods.
Presentation still counts
Fold the garment and band it in tissue so the flat bag arrives looking deliberate rather than cheap. Buyers notice packaging exactly once, when it fails.
Poly mailer questions
Is a poly mailer cheaper to ship than a box?
For the identical shirts on the identical lane it was, on every service quoted: the mailer’s best price came to $9.91 against the box’s best of $10.52 on 2026-07-27.
When is a poly mailer the wrong choice?
For anything crushable, rigid or fragile, for boxed collectibles whose packaging carries value, and for items with corners that could punch through plastic. Those belong in cartons.
Do all major carriers take poly mailers?
The quotes on this page came back from USPS, UPS and FedEx for a package described as a poly mailer, and bags move through all three networks daily. A strong mailer, fully sealed, is the expectation.
Can dimensional weight ever hit a mailer?
Practically no. The USPS trigger is one cubic foot, and a garment mailer runs far beneath it, so billing stays on scale weight. A bag stuffed to box-like thickness is the rare case that gets close.