Sterile Test Tubes With Two-Position Caps manufactured by Caplugs Evergreen are precision-molded from premium-grade, chemically inert plastic materials: polystyrene for clarity and polypropylene for toughness and chemical resistance. Polystyrene tubes withstand centrifugation to 8,200 × g while polypropylene tubes are almost transparent and withstand centrifugation to 10,000 × g. Overfitting caps have inner ribs for two-position fits: loose for aerobic culturing and tight for anaerobic culturing and sealing. Tabs and/or rings allow easy removal and sealing.