hybex Erlenmeyer Flasks are manufactured from high quality, borosilicate 3.3 glass. A low coefficient of thermal expansion (3.3), provides temperature resistance that is far superior to that of standard lab glass (or soda lime glass). Hybex glass is designed to withstand high temperatures, making them ideal for shaking applications, media preparation and long-term storage.The standard erlenmeyer flasks have permanent, white enamel graduations for volume measurement and a white identification box for marking or coding.For storage of media and cultures, the capped flasks include an autoclavable polypropylene cap & drip-ring. Optional cap colors are available, as well as PBT material caps for temperature applications up to 180C. (Threads are standard GL-45 for compatibility with a wide range of cap types from various manufacturers, including phenoic caps, vented caps, etc.)