This presentation describes an on-line technique for characterizing part shrinkage rate in the mold. Created to support the development of new polyolefin-based elastomers for injection-molded toys, the technique consists of measuring post-hold cavity-pressure decay rate inside the mold during the injection-molding process. The technique has been validated using a range of materials, including a semicrystalline polymer, an amorphous polymer, and formulated materials of varying complexities. It is believed that this technique can be a valuable tool for application development when a precise match of processing characteristics is desired for inter-polymer replacement.