Clear polypropylene vials with PP (polypropylene) lined, non-slit silicone septum screw caps. LCMS testing showed no presence of PFAS in the septum; suitable for low-level PFAS analysis. Septum thickness 0.040", durometer 35-60 for easy piercing. Reseals for repeat injections, unlike a membrane-type PE cap. Conical vial shape requires the needle stroke to be decreased by 3-4mm to prevent needle damage. For vials only, use 220-97331-60; for caps only, use 220-97331-91 (100/pk), 220-97331-92 (500/pk), or 220-97331-93 (1000/pk.)