Safety helmets for a wide range of conditions have become more effective by exploiting the availability of rugged lightweight plastics.
Whether constructing a building, or playing a game of football the safety of participants is of paramount concern. Helmets, an essential piece of safety equipment in numerous activities, have substantially benefitted from the development of plastics and composites by the chemical industry.
In order to protect the head from various injuries, helmets have evolved for specific functions. For bicycling, riders need lightweight, aerodynamic, and well-ventilated helmets, so a helmet’s construction typically contains a hard, polycarbonate shell lined with polystyrene foam for padding. Motorcycle helmets, although made from similar materials, do not require the same level of ventilation and instead must protect the head from higher energy impacts. As a result, engineers have designed a more closed style that features a Kevlar-reinforced fiberglass or Lexan shell. With both bicycling and motorcycling helmets the interior foam crushes upon impact cushioning the head, while the shell provides structure and helps repel more minor forces.
Helmets for football and ice hockey not only protect a player from impacts to the head, but also add protection for the face through a facemask or visor. The first football helmets made in the 1920s were sewn of leather and had limited padding inside; they did very little to reduce injury. Changes followed to create a more robust shell at first using stiffer leather. The biggest improvements came in the 1950s. With the introduction of polymers, designers adopted plastics for sports helmets.
Similarly, the development of fiberglass and high-density polyethylene (HDPE) transformed the hard hats worn by construction workers. Formerly they wore helmets made of metal. The new materials provide the same impenetrable protection, but of a much lighter weight material.
More information about helmets can be found at http://www.bhsi.org/howmade.htm, http://msf-usa.org/downloads/helmet_CSI.pdf, and http://www.popularmechanics.com/outdoors/sports/football/4281378.