Blown asphalt comes from hot air blown to pure bitumen in the last stage of refining. In this process, hot air having 200-300 degree centigrade temperature is blown to bitumen container with porous tubes. In this process, hydrogen atoms in bitumen hydrocarbon are combined with oxygen in the air and by forming water, polymerization happens. Compared with pure bitumen, blown bitumen has a low penetration rate and a high softness point. This kind of bitumen is used in making roof sheets, automobile battery, and coating.