Cool Medics M1824-BK-MDLG Helmet Liner with Neck Cover, Black, Medium/Large Cools up to 6 hours at 98 degrees Lowers Temperature on the inside of the liner by 20 Degrees Light weight and won't drip Great for cooling down firefighters coming off fire lines, construction workers, flight line personnel, where ever heat can effect how you work or play Reusable, immerse in water (10-30 seconds) to activate the cooling process