If you own a waterbed that has foam sides and looks like a regular mattress and the inside vinyl bladder needs to be replaced then look no further. All you have to do is measure the inside depth of your softside waterbed from the bottom of the foam to the top. This will tell you if you need a Deep Fill 7-9 inches, a Mid Fill 5-6 inches or a shallow fill 3-5 inches softside replacement mattress (bladder).