Bomex flask are made from quality borosilicate glass. It has many of the same qualities but is less expensive than Pyrex. This 1000ml boiling flask has a flat bottom along with a long neck and heavy uniform wall thickness. When using the boiling flask to heat liquid substances the bulbed bottom allows for heat to distribute through the liquid more evenly. It is marked with capacity and has an extra large marking spot. These are sold in packs of 6.