Test Tube Rack is molded from premium laboratory grade polypropylene, is dishwasher safe, disassembles for easy storage, and is autoclavable to 250°F. Plastic Flange Caps have two flexible flanges to help ensure a leak proof seal. Cylindrical Test Tubes made of PS material. Polystyrene Tubes are not autoclavable or dishwasher safe but are chemically resistant and clear like glass.