The TechNiche Phase Change Cooling CoolPax Extra Inserts with Hook and Loop Stabilizers are designed to provide continuous cooling relief for up to 3 hours. The outer material is made from high-quality, extra-strength polyurethane.  Features Phase Change Material cooling technology, which utilizes a carbon-based, non-toxic liquid that freezes at 58 degrees F and maintains the cool temperature for 2-3 hours. Hook and loop stabilizers help secure the insert packs in place.  These cooling inserts are compatible with Techniche vest models 6626, 6626I, 6626N, 6626HV, and 6627.