Preferred thermal stabilizers are 2-bromo-2-arylsulfonylacetamides, such as 2-bromo-2-p-tolysulfonylacetamide; 2(tribromomethyl sulfonyl)benzothiazole; and 6-substituted-2,4-bis(triboromomethyl)-s-triazines,such as 6-methyl or 6-phenyl-2,4-bis(tribromomethyl)-s-triazine.The thermally processable elements are exposed by means of various forms of energy.