Features of the TPP centrifuge tubes surpass ordinary tubes. They are: Manufactured with highest grade of raw material fulfilling requirements of USP Class VI The Max g force is 15,000xg (Product 91115 is polystyrene the max g force is 1,700 xg) White writing circle, affixed on the screw cap, for easy labeling with any writing instrument Caps that cannot be over-tightened Gas and aerosol tight cap Graduations all the way down to 0.5 ml Convenient racks available that are autoclavable and are collapsible for storage when not in use No additives, slip agents, biocides or plasticisers are employed By this we prevent leaching of substances into the valuable probes of the tubes.