A firm fitting, autoclavable, white culture tube cap made of non-absorbent polypropylene. Ribs inside cap provide a space between tube and cap to permit gas exchange between tube and atmosphere yet limit loss of media by evaporation. Caps are resistant to culture media, most acids, alkalis, alcohols, ethers, etc. Knurled edges facilitate handling. Top accepts wax pencil markers. Case of 1000.
