Contains 4 layers to the pads: 1. Fabric Release Liner - Hypoallergenic nonwoven layer provides breathable protection for sensitive skin. 2. Inner Layer - Hydrogel is highly heat conductive and allows for heat transfer from patient to the pad. 3. Insulative Outer Layer - Made of closed cell foam insulating the water from ambient conditions. 4. Leak Proof Technology - Negative pressure system prevent water escape if pierced or punctured. 1 pad individually wrapped.