TechNiche's Phase Change Cooling Vests maintain a comfortable 14 degrees C (58 degrees F) for up to 3 hours of critical heat stress relief. Size: M/L=100-175lbs L/XL=175-250lbs XXL=250-300lbs They are commonly used under high heat protective clothing, hazardous material suits, military body armor, and mascot costumes. TechKewl� Phase Change Cooling Vests keep you cool when you need it most! Avoid Heat Stress Stay Safe Great for Working Outdoors Works in extreme conditions Regulate Body Temperature TechKewl� Phase Change Cooling Vests are specially designed for long lasting durability in harsh working conditions. Vests have a comfortable v-neck design with a zipper closure. Hook and loop girth and shoulder adjustments provide a customized fit. V-neck w/zipper closure; hook & loop girth adjustments 100% cotton (excluding inserts) Thermal Liner Includes front chest pocket Include 1 set of 4 (Four) Cool Pax� 7065-V Phase Change Cooling Inserts How Phase Change Cooling Works: 1) Freeze Cool Pax� Ice Inserts (Included) 2 )Place in vest for hour of cooling 3) Frozen inserts provide extreme cooling effect Key Benefits of TechKewl� Phase Change Cooling: Provide cooling comfort and heat stress protection in high temperature environments. Commonly used in extreme heat under work gear, costumes, and other apparel. Phase Change Material releases long-lasting, temperature-specific (58 degrees F, 14 degrees C), cooling relief. Non-toxic, non-flammable, durable, reusable, lighter than water, and does not produce condensation. TechKewl� Activation & Use: Simply place in a freezer until solid. Or submerge inserts in ice water for up to 45 minutes. Place inserts to garment pockets. Wear comfortably; repeat steps as needed (or use additional inserts for continuous relief).