The flat bags we use are paper that is from the fabric printing industry. When they're getting ready to print on fabric they use paper first to make sure the registration and color is right, once that all checks out they switch to the cloth. In the old days they just threw that paper away, now they make it into bags.
Our frosted plastic bags are made from recycled milk bottles.
These bags are very sturdy. Sturdy enough that you can use them over and over again. A customer came in today that just returned from spending two years overseas. She said she used Carolina Creations black bags the entire time she was gone to carry her groceries home in from the store.