PTFE/Red Rubber. Seal 2000 is offered pre-inserted into an aluminum seal only. PTFE/Silicone Septa: (T/S) High quality, pure silicone is laminated to 0.005” thick PTFE to give a pure, highly inert septum with excellent resealing characteristics even after repeated punctures. PTFE/Silicone septa are the preferred product for use in most HPLC