A method is described for forming composite articles comprising thermoset silicon-containing polymers, that includes (a) providing a first composition comprising a first thermoset silicon-containing polymer; (b) providing a thermoplastic composition; (c) printing a first at least partial layer of the first composition comprising the first thermoset silicon-containing polymer using an additive manufacturing device; and (d) printing an at least partial reinforcing layer comprising the thermoplastic composition using an additive manufacturing device. Also described in an apparatus for preparing a composite article comprising thermoset silicon-containing polymers that includes an additive manufacturing printer having a printer drive mechanism, a first printing nozzle for forming a first layer of a first composition; and a second printing nozzle for forming a second layer of a second composition, wherein the additive manufacturing printer is capable of providing two or more layers of each of the first and the second composition to form a three-dimensional composite article of the first and the second composition according to a computer design model, and wherein at least one of the first printing nozzle and the second printing nozzle is a pressurized printing nozzle comprising a heating mechanism in operable contact therewith.