Three-dimensional decorative articles are produced from blanks of heat-shrinkable plastic sheet material, using a mold base having an outer surface with a recess over which a blank is placed, and a convex mold insert that moves into the recess by gravity as the blank softens and cooperates with the interior wall of the recess to shape the sheet material into a three-dimensional decorative article. A guide peg extends outward from the bottom of the recess past the outer surface of the mold base and extends through a hole formed in the blank, and through a guide hole in the mold insert to support the mold insert before heating and to guide the mold insert as it moves into the recess of the mold base.