A flask is a common piece of apparatus. Flasks can be found in almost every laboratory. A flask has a wider body at the bottom and a narrower neck with an opening at the top. Some flasks have more than one neck and opening at the top. Flasks are used to contain substances. Flasks are usually made of glass or borosilicate glass (Pyrex). Flasks can be used to heat the substance inside of them. There are several shapes of flasks.