… an envelope that you can put things in and mail The bubbles help protect the thing that you are mailing. It will not hold things that are bigger than the envelope. Do not let children or absurd adults "pop" the bubbles for fun as this will result in busted bubbles and result in no protection for your thing. Stock up on this essential item as you would canned goods and toilet paper. The #4 is the most desired-do not settle on anything less -you do not want to put your thing into a #2.