Light Weight Polyester blend Half-Head Sock: K1 Race Gear's K1 polyester blend half Head Sock is made of polyester fiber to absorb perspiration and wick the moisture away from the head. Thin material design for maximum breathability while retaining durability. Designed to only cover the racer's hair and back of the neck. You won't find a more comfortable and breathable balaclava than this one. Keep your Helmet Clean. Machine Washable.. Ultra-Lightweight Polyester Blend * Machine Washable * Fully Breathable for Comfort