AntarctechTM Phase Changing Cooling Blocks keeps workers cooler, safer and more productive by maintaining a 15 degrees C temperature for up to 4 hours once activated. The Antarctech Phase Changing Vest Blocks needs to be frozen for 2 hours before inserting in to the mesh pockets of the vest. Only to be used with the AntarctechTM Phase Changing Vest - Product Code: ATCV-V Ph7 Antarctech Phase Changing Vest Blocks