The invention relates to a method for in-situ synthesis of silicon nanoparticles in a thermosetting polymeric matrix, the thermosetting and thermoset matrices obtained in this way and a material including same. The method includes the following steps: a) forming an aqueous-phase/organic-phase inverse emulsion, wherein the aqueous phase includes at least a basic catalyst and the organic phase includes at least a non-cross-linked (co)polymer precursor chosen from an aliphatic, cycloaliphatic or aromatic epoxy resin precursor, a polyester-imide precursor, an unsaturated/epoxy polyester (co)polymer precursor, a polyether/epoxy (co)polymer precursor and a polyurethane precursor; b) introducing, into the inverse emulsion formed in step a), at least one silicon precursor forming a complete network whereof the rate of hydrolysis is greater than the cross-linking speed of the (co)polymer and c) stirring the mixture obtained in step b) and heating to a temperature between 20° C. and 70° C.