A method for preparing composite semi-finished products comprising an epoxy resin and a substrate, such as prepregs, syntactic foams, moulding compounds, synthetic marbles, said method comprising the steps of: - prearranging a container; - feeding a base epoxy resin into said container; - feeding into said container an anhydride cross-linking agent configured for reacting with said base epoxy resin to form a cross-linked epoxy resin; - feeding an amount of Titanium dioxide into said container; - feeding an amount of a radically polymerizable unsaturated reagent having at least one vinyl unsaturation into said container; - feeding an epoxy resin catalyst into said container, said epoxy resin catalyst configured for catalysing a reaction between said base epoxy resin and said anhydride cross-linking agent, so as to form a composition based on said base epoxy resin within said container, wherein said amount of Titanium dioxide is smaller than 16% by weight with respect to the total weight of said composition, said method comprising subsequent steps of: - bringing said composition into contact with a substrate selected between a plurality of reinforcing fibres and a mass of fillers, and - heating said composition up to a radical polymerization temperature of said radically polymerizable unsaturated reagent, whereby a step of a radical polymerization of said radically polymerizable unsaturated reagent occurs, so as to stabilize said composition in a semi-finished product comprising said substrate and said composition in a gel state. - prearranging a container; - feeding a base epoxy resin into said container; - feeding into said container an anhydride cross-linking agent configured for reacting with said base epoxy resin to form a cross-linked epoxy resin; - feeding an amount of Titanium dioxide into said container; - feeding an amount of a radically polymerizable unsaturated reagent having at least one vinyl unsaturation into said container; - feeding an epoxy resin catalyst into said container, said epoxy resin catalyst configured for catalysing a reaction between said base epoxy resin and said anhydride cross-linking agent, so as to form a composition based on said base epoxy resin within said container, wherein said amount of Titanium dioxide is smaller than 16% by weight with respect to the total weight of said composition, said method comprising subsequent steps of: - bringing said composition into contact with a substrate selected between a plurality of reinforcing fibres and a mass of fillers, and - heating said composition up to a radical polymerization temperature of said radically polymerizable unsaturated reagent, whereby a step of a radical polymerization of said radically polymerizable unsaturated reagent occurs, so as to stabilize said composition in a semi-finished product comprising said substrate and said composition in a gel state. - bringing said composition into contact with a substrate selected between a plurality of reinforcing fibres and a mass of fillers, and - heating said composition up to a radical polymerization temperature of said radically polymerizable unsaturated reagent, whereby a step of a radical polymerization of said radically polymerizable unsaturated reagent occurs, so as to stabilize said composition in a semi-finished product comprising said substrate and said composition in a gel state.