For use with 13-425 threaded caps or 13mm Snap/Crimp Caps, Thermo Scientific™ 13mm Septa are available in PTFE/ Red Rubber, PTFE/Silicone or Red PTFE/White Silicone/Red PTFE to suit a variety of applications. PTFE disk septa are chemically inert. PFTE/red rubber septa are economical for many GC applications. PTFE/silicone septa are most