The ready availability and low price of furfural, which is obtainable from annually renewable raw materials, and the ease of polymerization of this material by ionic catalysts, without the use of beat or pressure, suggested its use in the manufacture of low-cost casting plastics. It had previously been shown that the Incorporation of furfurin resulted in a material having satisfactory strength and appearance, but the material was unsuited for commercial applications because the mineral acids used as condensing agents continued to diffuse to the surface of molded articles over long periods of time;In this study, the effects of a large number of additive compounds other-than furfurin were investigated. It was found that best results were obtained by incorporation of a pair of additives. One additive was a form of lignin; the other was any one of a number of compounds falling Into two general classes. The first class was made up of secondary aromatic amines; those compounds from this class which were found to be most effective were furfurin, diphenyl-p-phenylenediamine, phenyl-beta-naphthylamine and diphenylamine. The second class was made up of furan derivatives whose substituent groups bad a relative electronegativity less than that of aldehyde group of furfural. Compounds from this class which were found to be most effective were furfurin, methylfuran, and furfuralurea. The furfuralurea was prepared in situ;It was found that the use of p-toluenesulfonic acid an a condensing agent resulted in a plastic which did not give the problems of acid diffusion which were encountered when mineral acids were used. The use of bromine also was a complete solution to the problem of acid diffusion, but the resulting product was limited in its applicability by a lower strength;The plastic resulting from the condensation with p-toluenesulfonic acid of the casting syrups described has a beautiful, glossy black appearance, remarkable flame resistances and good resistance to chemical reagents. It can be fabricated without expensive molding equipment, and is comparable in cost to the cheapest canting resins on the market today. This plastic should find use wherever an opaque, infusible, and insoluble material is suitable.