Description of Marmot Lost River Sport Tank - Women's Fast-drying, stretchy nylon make the Lost River tank an ideal top for long days out under a wide range of temperatures--works as well as a base layer in the morning as it does as an outer layer in the hot afternoon. Features: Main Material: 92% Cotton/8% Elastane Built-in Sport Bra M-Dot Logo Heat Transfer Nylon Supplex Yarn