Abstract: This invention is a formulation comprising a blend of a polybutene and an aliphatic lactate ester said blend containing from 50-99% w/w of the polybutene. The polybutene may be a poly-n-butenes, polyisobutenes, polymers containing a mixture of n-butene and isobutene monomer units, and mixtures thereof. The aliphatic lactate ester is suitably derivable from lactic acid and an aliphatic alcohol having from 6-10 carbon atoms. These formulations are particularly suitable for use as plasticizers for polymeric resins, especially copolymers of vinyl aromatics with acrylates and/or methacrylates such as e.g. a styrene/acrylate copolymer.