A process for preparing a composite material; the method comprises: a mixing step, during which a composition is mixed; the composition comprising from 2 wt% to 10 wt% of first inorganic particles, which have a size smaller than 0.1 mm and comprise a material selected from the group consisting of: silica, silicate; from 10 wt% to 30 wt% of an organic resin having a viscosity from 40 cps to 600 cps; from 30 wt% to 75 wt% of second inorganic particles, which have a size from 0.1 mm to 2 mm and comprise silica; from 3.25 wt% to 42 wt% of third inorganic particles, which have a spheroidal shape and a size smaller than 0.3 mm, wherein the spheroidal shape is defined as disclosed in the description from 0.08 wt% to 1 wt% of at least one silane having at least one vinyl moiety; and from 1 wt% to 6 wt% of at least one crosslinker; the sum of the weights of the first and third particles is from 5.25 wt% to 52 wt% of the composition; the sum of the weights of the first, second and third particles forming from 65 wt% to 85 wt% of the composition; a polymerising step, during which the organic resin polymerises together with the crosslinker so as to obtain the composite material; above 0.05 mm, the size of the inorganic particles means the diameter of such particles, which diameter is obtained by successive sieving with decreasing sieve hole sizes down to 0.05 mm; below 0.05 mm, the size of the inorganic particles means the mean diameter of such particles, obtained in accordance with DIN 50049 / EN 10204 by measuring the specific surface area BET as explained in the description; viscosity measurements are performed with a controlled rate rheometer as explained in the description; the first particles do not have a spheroidal shape; the third inorganic particles have a size of at least 0.01 mm; at least one third of the third inorganic particles have a size smaller than 0.05 mm; the third inorganic particles are made of glass; the second particles are made of a siliceous material selected from the group consisting of: quartz, fused silica, milled glass. a mixing step, during which a composition is mixed; the composition comprising from 2 wt% to 10 wt% of first inorganic particles, which have a size smaller than 0.1 mm and comprise a material selected from the group consisting of: silica, silicate; from 10 wt% to 30 wt% of an organic resin having a viscosity from 40 cps to 600 cps; from 30 wt% to 75 wt% of second inorganic particles, which have a size from 0.1 mm to 2 mm and comprise silica; from 3.25 wt% to 42 wt% of third inorganic particles, which have a spheroidal shape and a size smaller than 0.3 mm, wherein the spheroidal shape is defined as disclosed in the description from 0.08 wt% to 1 wt% of at least one silane having at least one vinyl moiety; and from 1 wt% to 6 wt% of at least one crosslinker; the sum of the weights of the first and third particles is from 5.25 wt% to 52 wt% of the composition; the sum of the weights of the first, second and third particles forming from 65 wt% to 85 wt% of the composition; a polymerising step, during which the organic resin polymerises together with the crosslinker so as to obtain the composite material; above 0.05 mm, the size of the inorganic particles means the diameter of such particles, which diameter is obtained by successive sieving with decreasing sieve hole sizes down to 0.05 mm; below 0.05 mm, the size of the inorganic particles means the mean diameter of such particles, obtained in accordance with DIN 50049 / EN 10204 by measuring the specific surface area BET as explained in the description; viscosity measurements are performed with a controlled rate rheometer as explained in the description; the first particles do not have a spheroidal shape; the third inorganic particles have a size of at least 0.01 mm; at least one third of the third inorganic particles have a size smaller than 0.05 mm; the third inorganic particles are made of glass; the second particles are made of a siliceous material selected from the group consisting of: quartz, fused silica, milled glass.