PP cap is made in one molded piece of inert, chemically resistant polyethylene. The starburst slits allows for easy needle penetration. Developed for high-sensitivity applications, especially in the LCMS Market, the purity of this cap for extractables is well below the picogram range. This highgrade polyethylene does not have the contamination issues PTFE/Silicone septa show at low levels of detection, while also sealing exceptionally well.