Parylene conformal coatings development started in 1947, when Michael Szwarc discovered the polymer as one of the thermal decomposition products of a common solvent p-xylene at a temperature between 700 and 900 °C. Szwarc first postulated the monomer to be para-xylylene which he confirmed by reacting the vapors with iodine and observing the para-xylylene di-iodide as the only product. The reaction yield was only a few percent, and a more efficient route was found later by William F. Gorham at Union Carbide. He deposited parylene films by the thermal decomposition of di-p-xylylene at 550 °C and in vacuum below 1 Torr. This process did not require a solvent and resulted in chemically resistant films free from pinholes. Union Carbide commercialized a parylene coating system in 1965.