M ODERN plastics are gaining popularity in industry because of the wide range of applications to which these materials lend themselves. In aircraft they are of immediate concern, because of advantages not found in other materials. While the application of plastics to aircraft structures is still in its infancy, and hence requires considerable discussion to qualify the contention, plastics have demonstrated superior characteristics in miscellaneous accessories used upon aircraft. The requirements for aircraft accessories include: noninflammability, flexibility, weather reistance, ease of machining, erosion resistance and good di-electric qualities. To these requirements may be added additional structural demands; high strength-weight ratio, freedom from shrinkage, smooth exterior .surface, ease of attachment or joining of parts, and low cost as compared with the present structural materials. No one plastic satisfies all of these requirements to the optimum advantage, but all may be met by careful selection of plastic materials from the large number which have appeared upon the market within the last few years. Whereas, prior to the expiration of the bakelite patents several years ago, bakelite and plastics were synonymous, the product bakelite is now one of many. The total plastic output in 1935 was 100,000,000 pounds with a valuation of $50,000,000. In 1930 it was but 31,000,000 pounds. Plastics are basically of organic origin, that is to say, they are combinations of carbon with hydrogen, oxygen, nitrogen, and other elements. A suitable classification of the plastic materials may be established by listing the products in accordance with their origin. This classification is important to those interested in plastics, as it arranges the large number of products into a more intelligible order. Particular attention is invited to groups I and II of Table 1, as these materials are used most frequently upon aircraft. In lieu of Table 1, plastic materials are classified sometimes by their behavior toward temperature. There are two groups comprising this classification: (1) Thermoplastic and (2) Thermosetting. A thermoplastic substance is rigid under normal temperatures and stress, but it deforms under heat and pressure. In this classification come the groups I, l ie, and III of Table 1. The thermosetting substances are initially thermoplastic, but in the process of applied heat and pressure they become permanently infusible, undergoing complete chemical and physical changes. In this classification TABLE 1