Septa are available in a variety of materials and thicknesses. PTFE Natural Rubber are moderately priced seals for GC and HPLC with good chemical properties. They are ideal for multiple injections due to high resealability, but not as easy to penetrate as PTFE/RR. PTFE/High Performance Rubber is a highly pure synthetic red rubber septum that provides a reduced background level for specific GC applications, employing sensitive detectors such as ECD or NPD. PTFE/Silicone Septa (T/S) has high-quality, low background/blank value, 100% synthetic pure silicone septa.