The chart indicates the synthetic resins which are thermoplastic, that is, which become plastic again upon reheating, and those which are thermosetting, that is, pass into an infusible stage at a certain critical temperature and pressure and do not again become plastic upon subsequent reheating. Sources of information. The data used in this report were obtained from a great variety of sources. The several American and British trade journals were freely consulted as were the various text books on this subject. Much of the information on the domestic industry was obtained by personal contact with producers and by correspondence. Field work included visits to most of the domestic producers of resins and a representative group of fabricators. Information of this type which was nonconfidential or which could be combined so as not to reveal individual operations was invaluable. Even where it was such that it could not be published it became part of the general background. The data pertaining to the industry in foreign countries were, for the most part, furnished the Tariff Commission by Department of Commerce representatives stationed abroad, in response to inquiries by the Commission. 2. SUMMARY Growth of the industry. The coal-tar synthetic resin industry in the United States began on a small scale some years before the World War. The output then was confined to a few types of tar-acid resins and the applications were quite limited until 1927, when certain of the basic patents expired. The output of about 1.5 million pounds in 1921 had increased to more than 13 million pounds in 1927 and the average unit value of sales had dropped from 81 cents per pound to 47 cents. Production continued to increase and the unit value to decrease annually until 1932 when general economic conditions forced a slight curtailment for 1 year. Since then the annual increase in volume and variety has been rapid. Production of non-coal-tar synthetic resins was started on a small scale in 1929 when both urea and vinyl resins entered the picture. Commercial production of the petroleum resins began in 1936 and of the acrylate resins in 1937. Table 1 shows the production and sales of coal-tar resins and of non-coal-tar resins, from 1921 through 1937. TABLE 1.—_Synthetic resins: United States production and sales, 1921-37_