A branched (co)polyformal is disclosed. The (co)polyformal contains structural units conforming to at least one the general formulae (1a) and (1b) ##STR00001## wherein each of -E- and -D- independently of one another denote an aromatic radical having 6 to 40 C atoms, k is 1 to 4,000, o is 1 to 4,000, m is z/o and n is (o-z)/o, where z is 0 to o.The branched (co)polyformal is characterized by its reduced water uptake and improved hydrolytic stability. Also disclosed are processes for its preparation and use in the production of molded articles.