The invention relates to porous dielectric layers obtained from pore-forming precursors and from matrix precursors. According to the invention, the pore-forming precursors used are chosen form molecules of myrtenol, ethyl chrysanthemumate, jasmine, trimethylbenzene, their positional isomers and their substituted or hydrogenated derivatives. The dielectric constant of the layer obtained is less than or equal to 2.5, starting from matrix precursors having a dielectric constant of less than or equal to 4.