20mL crimp-top headspace vial, flat bottom, clear 20mm x 3mm White PTFE/Silicone Septa with Alu CrimpReducing coring possibilities which prevents vacuum formation inside 20mm x 3mm White PTFE/Silicone Septa with Alu Crim, the Caps with Septa offered can successfully work over a wide temperature range and also come extensively lab tested for assurance of defined quality standards.