Because waterbed mattresses move (the "wave action"), hardside sheets often include features to prevent them from slipping off:
Purchasing waterbed sheets requires more precision than buying for a standard mattress because of unique sizing and specialized attachment systems. If you have a traditional waterbed (with a wooden frame), standard sheets will not fit. 1. Identify Your Waterbed Type buy waterbed sheets
Many waterbed sets have the flat sheet sewn to the fitted sheet at the foot. This "sleeping bag" style prevents the top sheet from being kicked off or lost in the frame during the night. 3. Sizing Guide for Hardside Waterbeds buy waterbed sheets