With PTFE / silicone seal made of PPS (polyphenylene sulphide). With PTFE / silicone seals having a particularly high level of mechanical resistance, even in temperatures up to 250°C. The non-slip, knurled outer surface ensures the screw cap can be closed securely and opened easily. The closure incorporates a PTFE-faced silicone seal wad and the substance in the container only comes in contact with PTFE. The silicone wad levels out any unevenness in the container neck.