These caps, made of polypropylene, are ideal for use with volatile solvents, sensitive compounds, and biological media. The SURE-LINK process welds each cap with a Polypropylene/PTFE/Silicone liner bonded to the cap. This process allows the cap to maintain seal through multiple autoclaving operations or cleaning procedures without the use of adhesives. Caps are ideal for storage of samples for prolonged periods of time. They are autoclavable at 121°C.