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