My mattress is 9 inches and had about 1 to 2 inches to play with zipping it up. I did wash it before I put it on the bed. Was a little bit more crinkly sounding than I thought it would be but be waterproof that's to be expected.  Since it has been on the bed a few weeks I don't even notice any crinkly sound. Maybe just needed to smooth out. Fit mattress perfect.