Chill-Its 6250 Clear Lightweight Phase Change Cooling Packs - Set of 4Ergodyne Ei 12120 The Chill Its Lightweight Phase Change Cooling Vest Packs are made to be inserted into model 6255 Lightweight Phase Change Cooling Vest to keep workers cooler, safer and more productive. The phase change cooling material in the packs is 100% biodegradable and maintain a 59 F (15 C) temperature for up to 2 hours when activated. These packs are designed to be 30% 60% lighter weight than other cooling vests on the market. HOW TO USE ***