Abstract: Method of preparing foamed solid aminoformaldehyde furfurylalcohol products by polymerizing a liquid furfurylalcohol containing aminoformaldehyde resin composition in the presence of an acid, characterized in using as a starting material a resin compositioncontaining 15-90% by weight of total free and bound furfurylalcohol and having an urea:formaldehyde molar ratio of 1:1 to 1:5 and at least 10 parts by weight of a boron compound per 100 parts by weight of said resin, the boron compound being present in an amount sufficient so that the foam product will pass the muffle furnace test at 500.degree. C., and has no second exotherm at 200.degree. C. The boron compound can be selected from the group consisting of boric acid, boron oxide, borax, boric acid esters, boron tribromide, boron trichloride, boron nitride, boron phosphate, boron trifluoride etherate, boron trifluoride methanol, boron trifloride monoethylamine, complexes of boric acid with polyhydroxyl compounds, and mixtures thereof.