Our personal cooling vest maintains a comfortable 65° F temperature for up to 3 hours. The semi-solid thermal energy storage material (PCM) is designed to absorb heat generated by the wearer. A great solution for working in high humidity areas and for use under other PPE garments where evaporative products are less effective.The PCM material is set at a comfortable temperature that will not cause vasoconstriction. Vasoconstriction is a physical response to extreme cold, where the veins and arteries constrict and slow blood movement, causing the body to retain heat. 65° is comfortable and less shocking to the body's system, allowing for natural circulation.