Reverse tuck mailers derive their name from the way the ends tuck into the box from opposite directions. Lightweight, sturdy kraft chipboard. Shipped flat. Easy to fold and assemble. Not intended to use as a shipping box. Designed to separate and protect items or as inner cartons. Dimensions when folded are 2.5″ X 2.5″ X 8″. Brand new, pack of 50. Non-smoking environment.