AllerSoft Zippered Mattress Encasings-fits Mattresses/Boxsprings up to 9". AllerSoft mattress encasings are made of a soft cotton blend 25/75 cotton/polyester material. A tight weave construction of 250 threads per square inch and requiring no membrane this material is a full proof barrier against bedroom allergens. In addition a double needle stitching and unique finish gives it a look and feel of cotton linens. It is both air permeable and water transmissive and comes with a rustproof polyester zipper which allows for easy removal when washing.