The jury is out until it's been used  for many nights to test the claims-- online header says 'waterproof' but package says 'water resistant'. (very diifferent meanings as you know it you're a parent with 'leaky' young kids or pets.)  It has 2 different fabrics zipped together to enclose the mattress completely. Topside is 2 layers-- upper top layer is 100% polyester that's coated with 100% polyurethane to 'resist water'  and 2nd top layer is soft, stretchy, semi-sheer poly that would NOT resist water. The under side of your mattress will rest on 1 uncoated poly layer of the  soft, stretchy, material.