A method is provided for making an annealed door skin or composite door assembly. At least the door skin is formed of a composition comprising a thermoset binder and fiberglass. The door skin, alone or in combination with other parts of a door assembly, is subjected to annealing to make the annealed door skin. The process of annealing comprises the step of heating the door skin, alone or in combination with other parts of the door assembly, above the glass transition temperature yet below the thermal degradation temperature of the thermoset binder for a sufficient amount of time to cause release internal stresses in the door skin, then the step of cooling the door skin.