A four-component resin system has been developed which exhibits improved surface quality and mold flow. The system consists of a monomer, an unsaturated polyester, a low profile additive, and an additional low molecular weight compatible compound. Systems of this type were found to have a synergistic effect in improving surface quality and mold flow. The characteristic of the low molecular weight compound that was found to be important is its ability to remain compatible with the curing unsaturated polyester and styrene.The Atryl® resin system is a combination of styrene, a propylene maleate unsaturated polyester, a saturated polyester thermoplastic, and one or more compatible compounds. The compatible compounds were selected from a wide range of low molecular weight materials. Numberous four-component resin systems have been prepared and evaluated in SMC. The surface quality and physical properties have been found to meet or exceed automotive specifications.