Wheaton screw caps, white, 22-400 cap, pp, white, ptfe/ silicone liner .060 use these caps with numbered glass bottles or vials white polypropylene screw cap provides clear surface for writing on cap these polypropylene autoclavable solid top caps have a bonded ptfe faced silicone liner making them ideal for storage and retrieval of volatile solvents, sensitive compounds and corrosive chemicals the liners consist of 0.055″ (1.4 mm) of silicone and 0.005″ (0.14 mm) of ptfe. Warning: this product can expose you to chemicals including tetrafluoroethylene, which are known to the state of california to cause cancer. Prop 65 warning