Merrell Opti-Wick fabric transfers moisture away from your skin and dries quickly to keep you comfortable. 100% polyester. 20+ UPF fabric. Our most technical, run-able style. Two-sided, double-knit mesh. Set-in sleeves. Reverse contrasting side panels and flatlock stitching eliminate side seams and chafing. Forward shoulder seam eliminates high friction rub under straps. Reflective logo for visibility.