A grauated cylinder (also called measuring cylinder or graduated glass) is a piece of laboratory glassware or plasticware used to accurately measure out volumes of chemicals for use in reactions. They are generally more accurate and precise for this purpose than flasks. Often, the largest graduated cylinders are made of polypropylene for its excellent chemical resistance or polymethylpentane for its clarity, making them lighter to ship and less fragile than glass. Polypropylene cylinders have excellent chemical resistance and do not shatter when dropped, a valuable safety feature for all laboratories. Polypropylene is easy to repeatedly autoclave (sterilize). Often used for collecting and recording a volume of gas given off in a reaction.