Septa for the original wide-opening vials from MicroLiter are ideal for chromatography applications where vials remain stationary.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