"Don't let the pretty colors fool you! These conical 15mL and 50mL centrifuge tubes are made of premium polypropylene, with exceptionally uniform wall thickness for clarity and centrifugal strength. Tubes and caps may be used for sample storage at temperatures as low as -86°C. The maximum centrifugal forces are 12,000xg for the 15mL tubes and 15,000xg for 50mL version.* Tubes and caps are suitable for stem cell research and certified sterile, RNase, DNase, and Pyrogen free. *Refers to liquids with a specific gravity of 1.0, using appropriate rotors, cushions and adapters. Color coded caps for easy sample identification 15mL rated to 12,000xg 50mL rated to 15,000xg Sterile, RNase, DNase, pyrogen and cytotoxin free Sterile (gamma) and individually packed Leak Proof"