Polyester and polypropylene are both acid-free synthetic materials, both particularly adapted for photo storage and archival.
- Polyester : Polyester is very strong and will withstand heavy use. It is very hard to puncture and tear, and highly transparent.
- Polypro : Polypro is a softer, more flexible material than polyester. It is more economical, but does not offer the same strength, durability and transparence as polyester.