There are three levels of creosote:
Level 1: creosote is usually a light powder or soot and can easily be removed.
Level 3: The most severe and challenging form of creosote is level 3. It is extremely thick and hardened. It is similar to tar. Level 3 creosote is extremely difficult to remove and poses a severe fire hazard.
Level 3 creosote is also called glazed creosote. It forms when creosote rapidly accumulates in the flue before the previous layers have dried. As it hardens, glazed creosote dries into a hard, dense substance that can damage the flue and chimney structure. Glazed creosote can be caused by burning unseasoned wood or by burning a fire at a low temperature for a long time.