These Reagent Bottles are made from the same laboratory borosilicate as our Erlenmeyer Flasks. No silicone o-ring required. These 500ml Regent Bottles are ideal for the boiling and storage of wort for your starter, or transporting yeast from yeast starters. Simply place in microwave to sterilize wort then cap and put in fridge until you need to make your starter. The whole bottle can be autoclaved. Safety warnings:**Please still exercise care when handling these and any other Borosilicate glass.**There is a common misconception that Borosilicate glass is virtually bulletproof and can handle any dramatic temperature that is thrown at it. This is not strictly true.Though it does have an incredible ability to withstand sudden and drastic temperature shocks compared to your average soda-lime glass, it should still be treated consciously with care.Cool all glassware slowly to prevent breakage, unless you are using VYCOR glassware which can go from high heat to ice water with no damage.Do not take your boiled flask directly from the stovetop straight into a bath of ice water. Though some people do this without failure, borosilicate glass is not designed for such an application. Please allow the flask to cool for a few minutes before running under water, before placing into an ice bath; the slower you introduce your flasks to temperature changes, the longer it will last. Going from fire to ice in a matter of seconds will introduce incredible amounts of stress to the glass structure. While the glass may be able to withstand this some of the time, other times you may not be so lucky. If the temperature differential is big enough, it will shatter. All Borosilicate glass will break eventually after a number of heat/cool cycles, it is impossible to give an exact number to determine when, but this is a natural an inherent feature of the material.Please do not boil your flasks dry or dry them out using a stove. The temperature for drying should not exceed 140°C, which a naked flame can easily exceed.Do not heat glassware that is etched, cracked, chipped, nicked, or scratched. It is more prone to break.Do not heat glassware directly on electrical heating elements. Excessive stress will be induced in the glass, and this can result in breakage.Please read and heed these guidelines, as KegLand do not warrant mishandling of borosilicate glassware.