Blends of unsaturated polyester, styrene and polyvinyl acetate are hot cured either between glass plates or under pressure in a molding simulator. The morphologies of the products are observed using microscopy and show their usual aspects. They are characterized according to fractal concepts by image processing; the influence of mixture composition, pressure and temperature is investigated. Based on the hypothesis that phase separation governs the shrinkage compensation, a computer simulation of the fissuration phenomenon is performed using the diffusion limited agregation (DLA) model. This fractal model gives realistic results, and is used to show the effect of network parameters on the fissures fractal dimensions.