Wheaton White Polypropylene Screw Caps have a bonded PTFE faced silicone liner making them ideal for storage and containment of volatile solvents, sensitive compounds, and corrosive chemicals. The liners consist of 1.4mm of silicone and 0.14 mm of PTFE. Can withstand autoclaving / sterilizing. Screw caps are frequently used with Wheaton E-Z Ex-Traction High Recovery Vials (Nos. W224601, W224603, W224613, W224617, W224618, W224619, W224630, W224632, W224634, and W224636.