A mathematical model that describes the effect of conversion and polymerization temperature on the porosity of suspension poly(vinyl chloride) is proposed. The model considers that the packing of the primary particles that develop in the polymerizing drop begins at a conversion at which the particles become motionless. The model considers the morphology of the primary particles as a group of particles with a particular sphericity that,form a network whose porosity decreases as conversion increases. Furthermore, the model considers the effect on porosity of the desorption of residual monomer and the difference in contraction and deformation between the pericellular membrane and the network of particles. The model contains three parameters that are estimated from data reported in the open literature. The agreement between experimental data and the theoretical predictions of the model are satisfactory. (C) 2004 American Institute of Chemical Engineers.