For best deliverability, use light-colored, non-glossy or uncoated paper. Avoid transparent, fluorescent, heavily textured, dark fibers or background patterns in your paper choice. Poly wrappers or shrink wrappers are not acceptable. Use low reflective window envelopes.
Use a sealable envelope or tabs, wafer seals, tape strips, or spot glue to close mail pieces. Do not use clasps, staples*, string, or buttons on letter-size mail. Note: The required number and location of tabs, wafer seals, tape strips, or spot glue varies with the type of mailpiece and the paper used.
* If staples are used to attach multiple sheets, the mailpiece must be folded so no staples appear on the outside.