The model previously proposed to predict the volume change of filled blends was extended to unsaturated polyester/styrene blends without or with thermoplastic additive and to blends with fillers and/or fibers. This model was based on experimental results from Pressure Volume Temperature X (PVTX) setup where temperature, conversion degree, and volume at a controlled pressure were monitored simultaneously. Predictions obtained from the model were compared to experimental results and were in good agreement. This model took into account thermal expansion, polymerization shrinkage, and shrinkage compensation via porosity formation. These phenomena were deconvoluted from the experimental curve and separately quantified. It was shown that shrinkage and its compensation induced a volume variation exhibiting a linear dependence with conversion degree. The influences of low-profile additive content, pressure, fillers, and fiber presence on shrinkage control were highlighted. (C) 2004 Wiley Periodicals, Inc.