The flat bottom flask is likely the other round bottom flask but with a flat bottom allowing it standing up flat surface as the flask can sit upright on its own. Capacity of 250mL with 24/40 glass ground taper joint. It can be used in heading during distillation, they are not as durable as round bottom flasks for heating better than Erlenmeyer flask which has have the sharp and vulnerable corners .Proglass flasks are heavy wall design, made by hand-blowing to ensure uniform wall thickness, and made of high-quality borosilicate glass and annealed at 800 degree Celsius, can be heated directly in an open flame and can withstand typical laboratory thermal variations in Chemistry processes like heating and cooling.