These pillow protector covers are made of washable polypropylene fabric material. 4 covers per pack. Designed to fit standard pillows (Approx Size: 21" x 27" / 50cm x 70cm). These pillow covers are Strong, Stain Resistant, Machine Washable and Mildew Proof. The material appears to be a polypropylene spunbonded non woven fabric (the type of material used as head rest covers on aeroplanes) this makes the fabric breathable, soft, light, chemical resistant, nontoxic and environment friendly. Please note that while these pillow protectors will help to prevent sweat stains etc, they are not waterproof.