The flexible sealing lip inside the cap ensures a positive leakproof seal under even the most adverse conditions. This deep internal lip fits snugly against the interior wall of the tube preventing the contents from coming in contact with the threads, thus reducing the chances of sample contamination. This series of tubes is available either plain or with printed graduations and white marking area for sample identification. Caps are supplied with attachment loops in order to prevent contamination and mix-up. These microcentrifuge tubes have all the other fine features stated in the introduction page, but cannot be autoclaved since closure is made of high density polyethylene. Non skirted tubes can be centrifuged up to 20,000g. Skirted tubes can be centrifuged up to 17,000g. Will withstand temperatures from -196°C (vapor phase) to +110°C. Tubes and caps are certified RNase, DNase, DNA and Pyrogen free.