Designed by the wind and built for high-speed activity, the SUN BLADE^™ Hat With Mesh maintains superior UPF 50 sun protection while other hats are blown away. No more flip-flopping with every breeze! Our flexible, foam brim features a two-way, deep-curve design that keeps your hat on top where it belongs. The strategically placed 3D mesh keeps fabric off your skin and provides cooling ventilation.SizingS/M circumference is 57cmL/XL circumference is 59 cm