The tubes are made for repeated cap closures and eliminates pressure induced popping of caps during incubation. Our tubes can be used at temperatures from +121C to -80C and an RCF of 17,000xg. Superior clarity and external graduations ensure accurate, reproducible lab results. All tubes are made with virgin natural polypropylene, and free of RNase, DNase, and non-pyrogenic. All tubes have flat cap and frosted side for marking with markers. Available as natural and assorted colors.