Industrial grade bitumen is also known as blown bitumen. This is obtained by blowing air into hot bitumen at high temperatures (normally beyond 180º C). Blowing hot air into bitumen at high temperatures results in structural changes in bitumen. Esters are formed in this process and these esters link up two different molecules and higher molecular weight material increases drastically. In the process the asphalting content is increased which in turn results in higher softening points and very low penetration number. Industrial grade bitumen is used in industrial applications and in water proofing, tar felting etc.