Boiling flask. It is an important type of flask used in laboratories for heating substances that need to be heated evenly. It is a laboratory glassware used as a container to hold solutions of chemicals. Boiling flasks have a round body with a single long neck. They come with either a flat bottom or round bottom. Boiling flasks with round bottoms need some sort of support to stand upright while the flasks with a flat bottom can stand upright alone on a flat surface.