Hybrid stretch up to 15" - Knit fabric w/ urethane top and bottom - Self-Locking Zipper w/ unique patented tape closure to form a complete seal preventing bed bugs from getting in or out - Easy to install for 6" or 9" deep mattresses. Fully waterproof top, bottom and sides - Breathable design - Dust Allergen Proof - Laboratory tested and certified bed bug proof !! Lab results available upon request - Machine Washable for re-use