A structural ice mold of the large, single use type, preferably made of FDA approved low density polyethylene plastic, is rotationally molded into a shape forming a hollow cavity on the inside thereof which defines the ice sculpture or figurine to be formed therein. In the improvement of the invention a narrow peripheral ridge or U-shape rib is extended vertically around the outside of the ice mold, preferably at the parting line of the permanent parent mold. The one-piece mold may be opened at the U-shape rib by cutting across the side of the rib at positions away from the surface of the ice figure formed in the mold, rather than by cutting perpendicularly through the mold surface and potentially into the ice figure therein. An additional improvement in ice molds resides in a hollow core formed in the base of the mold which allows for expansion of water in the mold when it changes phase into ice, thereby reducing stress and cracking in the finished ice form.