These are professional mail bags used for mailing things such as t-shirts. When you ship a t-shirt with this mail bag, it qualifies as a letter, so it's super cheap to send out your merch! Buy as many bags and labels as you want, and ship out shirts as they're ordered.
Simply fill out the shipping label, slap it on the bag, slide in the ordered shirts, close it up and drop it off at the post office.
Plenty of room for you to slide in a CD or stickers etc as well!