A process for the manufacture of flame-resistant threads, fibers, and films and the like products that contain a synthetic polymer and cellulose, which comprises processing a mixture of viscose and an aqueous alkaline solution of a polyacyloxalamidraxone such as polyterephthaloyloxalamidrazone to form a thread or like product, immersing the product in a treatment bath that can be neutral acidic or alkaline in which bath it is allowed to react with a solution of one or more metal compounds, e.g., zinc chloride, tin chloride, and/or barium chloride, and thereafter washing and drying the resulting product.