A molding assembly for high temperature composite articles utilizes low temperature inflatable mandrels to produce composite articles from a thermoforming compound. The molding assembly includes a first mold form, a second mold form, at least one inflation adapter, and a mandrel bladder. The first mold form and the second mold form each comprise a molding recess to mold the thermoforming compound as the thermoforming compound is heated. The mandrel bladder is pressurized to inflate and press the thermoforming compound against the first mold form and the second mold form. Each inflation adapter comprises a mandrel conduit and a cooling conduit. The mandrel conduit allows for the inflation and deflation of the mandrel bladder. The cooling conduit allows for a stream of coolant to flow adjacent to the mandrel bladder to prevent structural degradation of the mandrel bladder from the temperatures necessary to transition the thermoforming compound into a fluid.