Transparent. Polysulphone (PSU) with PP screw cap. As stable and robust as PC test-tubes, but considerably more resistant to acids and alkalis. Autoclavable. Can be used in refrigerated or ambient centrifuges at up to 50000xg rcf. Accessory sealing cap assemblies are available for all sizes. Notes: If autoclaving, the tubes must be filled to 80% of their total capacity. Polysulphone must not be used with Tween, as this causes hairline cracks to form.