Florence Flask. A Florence flask (also known as a round bottom flask or a boiling flask) is a piece of laboratory glassware. It is a round or flat-bottom flask with a long neck. It is designed for uniform heating and is produced in a number of different glass thicknesses to stand different types of use. They are often made of borosilicate glass that has alkali to prevent cracks or defacing of the glass. The flask is named after Florence, Italy..