Erlenmeyer flasks are used to measure, mix, and store liquids. The shape makes this flask very stable. They are one of the most common and useful pieces of chemistry lab glassware. Most erlenmeyer flasks are made of borosilicate glass so that they can be heated over a flame or autoclaved. The most common sizes of erlenmeyer flasks probably are 250 ml and 500 ml. They can be found in 50, 125, 250, 500, 1000 ml. You can seal them with a cork or stopper or place plastic or paraffin film or a watch glass on top of them.