Costar® microcentrifuge tubes are made of polypropylene and are certified RNase-/DNase-free. Tubes are supplied nonsterile and are autoclavable. External graduations and frosted writing spot for easy sample identification. Positive seal design allows for repeated opening and closing. Flat cap surface for convenient labeling. Withstands a maximum RCF of 17,000 x g. Rainbow pack includes one bag each of blue, green, yellow, red, and orange tubes.