Improved impact strength, flexibility, and melt flow are among the properties that polybutenes are capable of imparting to thermoplastic polymers. Here, the author discusses as study in which two types of acrylonitrile-butadiene-styrene (ABS) resins-an emulsion and a bulk/mass product-were fortified by the addition of increasing levels of polybutenes. Compounding and testing methods, and the effect of polybutene concentration and molecular weight on properties of the blends, are described.