The invention provides a mold for use in a compression molding apparatus that has a frame part (41) with a hole through its center; a bottom plunger (42); and a top plunger (43); wherein the plungers are fabricated to fit substantially snugly in the hole in the frame part, and wherein at least one plunger comprises at least one low-thermal conductivity insert (44, 44'). The mold is useful in compression molding processes used in the preparation of unitized membrane electrodes.