Frequently Asked Questions - About.usp…
https://about.usps.com/postal-bulletin/2007/html/pb22218/kit1_021.html
Large envelopes as well as padded mailing bags must be somewhat flexible (not rigid) and uniformly thick. Items mailed in large envelopes cannot have more than a 1/4 inch variance in thickness. Mailpieces must be rectangular with a maximum thickness (at the thickest point) of 3/4 inch. USPS provides free shipping boxes and envelopes for Priority Mail and Global Express Guaranteed packages. Padded envelopes cost $0.55 in additional postage. You can find USPS padded envelopes at USPS online stores, your local post office, and other shipping supplies locations.
Large envelopes as well as padded mailing bags must be somewhat flexible (not rigid) and uniformly thick.
Items mailed in large envelopes cannot have more than a 1/4 inch variance in thickness.
Mailpieces must be rectangular with a maximum thickness (at the thickest point) of 3/4 inch.
USPS provides free shipping boxes and envelopes for Priority Mail and Global Express Guaranteed packages.
Padded envelopes cost $0.55 in additional postage.
You can find USPS padded envelopes at USPS online stores, your local post office, and other shipping supplies locations.
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