The physical properties of synthetics are essentially those of the polymers from which they are made. The king of the polymers is polyethylene, or PE. It is produced in the highest volume globally and its production (or consumption!) is considered a measure of industrial growth.
The second most common polymer in the world is polypropylene, or PP. According to a report from GBI Research, the global PP market is predicted to reach 62.4 million metric tons by 2020. In terms of end-use consumption, construction currently accounts for 5 percent of the PP market.
E.W. Fawcett and R.O. Gibson of Imperial Chemical Industries in London discovered polyethylene accidentally, in 1933, when they reacted ethylene at extremely high pressures. However, large volume production did not become economically viable until catalysts were developed to control the way carbon compounds are fabricated into materials on the molecular scale.
German Karl Ziegler discovered the first titanium-based catalysts, and Italian Giulio Natta used them to control the growth of polypropylene polymers. These two chemists were deservedly awarded the Nobel Prize in Chemistry in 1963 for the development of Ziegler-Natta catalysts, the workhorse in the commercial manufacture of various polyolefins since 1956. They ushered in the age of plastics by allowing for the production of plastics on a grand scale.
For more about the raw materials used in the manufacture of synthetic underlayments, see Tarco's white paper “Rethinking Roofing Underlayments.”