? The exact composition of a particular shingle depends on the manufacturer and the
roofing application, but the shingle manufacturing process is similar in each instance.
The process begins with a layer of organic (cellulose or wood fiber) or fiberglass
backing felt. The felt is impregnated with liquid asphalt, then coated on both sides with
additional asphalt. The asphalt used as the saturant is of a different type than the asphalt
used as the coating, but both are harder than asphalt generally used in pavement. Both
types of asphalt are “air-blown”, or bubbled, during production, a process that
incorporates oxygen into the asphalt and further increases the viscosity. Powdered
limestone (70% passing the No. 200 sieve) is also added to both types of asphalt as a
stabilizer.