Except for pressure-sensitive filament tape, tapes used for closure and reinforcement should be at least 2 inches wide.
Nonreinforced plastic tapes must be at least as strong in the cross direction as in the machine (long) direction.
Twine or cord should not be used for closure and reinforcement, as it could interfere in mail processing equipment.
Loose strapping and metal strapping are not acceptable.
Plastic bags must be at least 2 mil thick polyethylene or equivalent for easy loads up to 5 pounds; 4 mil thick for easy loads up to 10 pounds.
Heat-shrinkable plastic film—either irradiated polyethylene, linear low-density polyolefin, or copolymer—may be used as packaging for mailpieces under the following conditions only: Cloth bags are acceptable for easy and average loads of up to 10 pounds, if the seams of the bags equal the strength of the basic material.
Mailable aerosol containers must be packaged under Publication 52, (PUB 52) part 342.
Mailpieces containing perishable, hazardous (including infectious substances), biological, or restricted materials are subject to the standards in PUB 52.
Mailers must adequately stabilize heavy items within the package.
A strong packaging or paper tape (not cellophane or masking tape) may be used for the closure or reinforcement of packages.
If an odd-shaped item is not properly wrapped, it could burst through the envelope and cause injury to employees and damage to USPS processing equipment.
Odd-shaped items that are properly wrapped within paper envelopes and sent at letter prices may be subject to the nonmachinable surcharge under Aerosols (containers under pressure) are hazardous materials and must be constructed to prevent accidental discharge of the contents during postal handling.
Mailers may use staples or steel stitching to close boxes as follows: For easy loads of up to 5 pounds, paper bags and wraps are acceptable when at least of a 50-pound basis weight (the strength of an average large grocery bag) and the items are immune from impact or pressure damage.