Polystyrene. Non-toxic to cells in culture techniques. Polyethylene plug seal screw caps provide a tight closure. Printed with dark blue graduations. White writing patch. Radiation-sterilized. Racked tubes are supplied in polystyrene racks. Tubes withstand 1800 g (15 ml) and 2000 g (50 ml). Dimensions: 17 x 120 mm for 15 ml tubes and 30 x 115 mm for 50 ml tubes.