A test mold assembly for evaluating the surface deformation tendency of a coverstock bonded to a reactive plastic formulation to voids in the formulation including a base adapted to support a coverstock and spaced side walls extending upwardly from the base to define a mold cavity for receiving foam precursors. The assembly further includes a lid adapted to form the top of the mold cavity and having a cover portion disposed spaced from the base. The lid includes a plurality of integral projections extending downwardly from the cover portion into the mold cavity a predetermined distance to create voids in the foam. A method of making a foam void model for evaluating the surface deformation tendency of a coverstock bonded to a reactive plastic formulation to voids in the formulation is also disclosed.