The Outdoor Research Sun Runner Cap is a versatile cap that has a removable, adjustable skirt that gives you shelter from harsh rays or can be removed when you just need ball-cap coverage.The lightweight Sun Runner Cap fabric provides UPF 30+ sun protection. Mesh side panels let air flow over the sides of your head.Features: Breathable Lightweight UPF 30 Multiple Configurations for Variable Protection Levels Snap-On Sun Skirt Plastic-Stiffened Brim Wicking Headband Breathable Mesh Panels External Cinch-Strap Adjustment Removable Chin Cord Avg. Weight: 2.8oz Fabric: Main Body: 100% Supplex nylon, plain weave Mesh Sides: 100% polyester Measuring Guide: (Measure around head where headwear would fit comfortably) Small: 6 7/8 = 21 5/8" Medium: 7 1/8 = 22 1/2" Large: 7 3/8 = 23 1/4"