CUSTOMIZABLE COMFORT FOR A PERFECT FIT. The black underbill on the Nike Sportswear Aerobill Featherlight Cap helps reduce glare so you can see more and squint less. Sweat-wicking fabric and mesh inserts help keep you feeling cool and comfortable throughout the day. This product is made with at least 75% recycled polyester fibers. Benefits: Nike AeroBill technology combines breathability with sweat-wicking comfort. Mesh panels enhance breathability. Back closure adjusts for a customized fit. Product Details: Fabric: 100% recycled polyester. Hand wash. Imported. Style: 679421; Color: White/White/Black/Black; Size: One Size; Gender: Unisex; Age Group: Adult | Nike Sportswear AeroBill Featherlight Adjustable Cap in White, Size: One Size | 679421-104