The primary reason that asbestos was used in building products was as a binder or filler material. It was cheap and easily available. It is stringy and resilient, and thus made a good binder. Its resilience also reduced the breakage of the products between the factory and the worksite. In pipe covering and other materials, asbestos created air pockets which provided heat resistance.
Asbestos was marketed for its "fire resistant" qualities. In reality, at approximately 1200 degrees, asbestos transforms into an inert mineral. Other materials were available, even in the 1930's and thereafter, that could have been used (and, in fact, were used) as substitutes for asbestos without any sacrifice in product integrity or heat resistance. The asbestos industry peddled asbestos as a "magic mineral," creating a demand for the material, without advising of the dangers of asbestos. As a result, thousands of American workers were injured and killed. It was unnecessary and could have been avoided.