These Narrow Mouth Reagent Bottles are available in Polypropylene as well as Polyethylene. The PP bottles are rigid, translucent and have excellent contact clarity. These bottles can be autoclaved f illed as well as empty. On the other hand, the Polyethylene bottle too have excellent strength and are unbreakable. The Polypropylene Cap has a built in seal ring to make thesebottles leakproof. Material: Polypropylene