Sparco Short Sleeve Micropoly Kart Top, Knit 4-ways stretch Outside 77% polyester; 23% polypropylene microfiber in contact with skin. Polypropylene: the lowest specific weight among the textile fibres. Dry fast: polypropylene is hydrophobic and keeps the moisture away from the skin; the special structure of the knit allows fast evaporation. Anti-bacterial permanent treatment: inhibits the growth of odor-causing bacteria. Easy care: do not iron!