These polypropylene caps have excellent sealing characteristics and offer good chemical resistance including acids, alcohols, alkalis, aqueous products, cosmetics, and household oils. Polypropylene Hole Caps are known for good impact strength, cost effectiveness, and pliability. Septa sold separately.Polypropylene hole caps are available preassembled with separate septa or without septa. We also feature polypropylene hole closures with bonded septa to provide assurance that the septa will not slip away from the cap while injecting.