A dilatometer, designed and built in-house, was applied to the study of low-profile unsaturated polyester resins. The change in polymer morphology as a function of polymerization shrinkage and low-profile additive (LPA)-induced plateau region, and the role of fissure formation in the LPA mechanism were investigated. An LPA mechanism was proposed based on the findings of this study., Also included in this work was the effect of pressure and thickening on shrinkage control. Finally, a series of bulk moulding compound compression mouldings was performed to investigate the relationship between polymerization shrinkage control and moulded panel surface quality and moulding shrinkage.