From the manufacturer:
The ArtEnvelope PRO is designed to withstand the elements better than inexpensive paper-based envelopes. The gloss black water-resistant exterior is made from a coated non-woven polypropylene material. It is ideal for transporting presentation albums to and from school, the office or to important meetings. The textured interior is also delicate enough for carrying and storing artwork, paintings and photographs. The strong perimeter stitching and durable black comfort handles support long-term use and the light-weight construction makes it easy to carry.