Sterile, bulk pack, blue With the securely sealing Thermo Scientific Nalgene serum tube closures made of high-density polyethylene (HDPE) with a continuous thread and insert, you can achieve a leak-proof seal even without a rubber stopper. Features: Sterile up to 10 -6 SAL Insert with a core made of low density polyethylene (LDPE) between two layers of solid HDPE and closures available in different colorsMeer tonenMinder tonen