Abstract: A process for obtaining fiber-reinforced foams suitable to be transformed to reinforced solid cellular materials having a density lower than 0.7 kg/l, if inert fillers are not present, and lower than 1 kg/l if inert fillers are present as well, essentially by mechanical incorporation of gas or a mixture of gases into an unsaturated polyester resin containing conventional additives is described. As reinforcing materials synthetic, vegetable or mineral fibers having a maximum length of 3 mm are employed. The mixture of the resin with the fibers, and optionally with the inert fillers, is conveyed by at least one pump to a mechanical foaming device which introduces into the mixture gas in form of small bubbles, homogeneously and uniformly distributed therein.