usps approved poly bags

The listings consistently identify the poly mailers as made from polyethylene.

Padded mailers include an inner layer of bubble cushioning for extra protection. They’re also described as moisture-resistant and tamper-evident, helping protect semi-fragile items during transit.

Yes—some listings provide both inside and outside measurements. For example, a #6 mailer is shown with inside dimensions of 14.5 × 19 in and exterior dimensions of 14.5 × 20.5 in.

Several descriptions call the mailers waterproof or moisture-resistant and puncture- or tear-resistant. Thicker constructions (notably 3 Mil) are specifically noted as better at resisting punctures and tears.

Pack counts shown in the results include 3, 100, 250, and 500 per pack.

Expandable (gusseted) mailers have a bottom gusset for extra internal space—listed as roughly 20–40% more capacity. Descriptions also note they can be made 3 Mil thick for added puncture/tear protection and commonly list water resistance and a self-sealing closure.

Self-sealing strips let you close mailers quickly without additional tape, speeding packing. Listings commonly call the closure a peel-off or peel‑n‑seal strip, and some descriptions note the seal is tamper-evident.