Silicone/PTFE Seals The special, slitted liner for VWR (Merck®)/Hitachi is only available unassembled, as the diameter with the most optimal valve effect does not achieve any press-fit in the cap. Enlargement of the diameter is only possible with negative effects on the building up of vacuums in the vial. • Temperature resistant from -60°C up to 200°C. • Silicone liners with PTFE on both sides for less coring. • Much cleaner than Natural Rubber, RedRubber or Butyl. • Different hardnesses (durometers) to meet requirements of the various types of needles regarding penetration.