Round-bottom flask

Round-bottom flasks and cork rings

Laboratory distillation set-up using a Liebig condenser, without a fractionating column. Both distilling (left) and receiving (right) flasks are round-bottom flasks.

Round-bottom flasks (round-bottomed flasks or RB flasks) are types of flasks having spherical bottoms used as laboratory glassware.

They are used mostly for chemical or biochemical work. Today, they are usually made of heat-resistant borosilicate glass. There is at least one tubular section known as the neck with an opening at the tip. Two or three-necked flasks are made. Round bottom flasks come in many sizes.