The present invention relates to thermosetting impermeable coatings capable of being obtained by the deposition of a precursor solution, of use for guaranteeing the impermeability of composite structures, in particular in the aeronautical, railway, motor vehicle, nautical, naval, wind power and construction fields. The invention also relates to a process for preparing said coating. The invention also relates to a process for preparing a precursor solution, and the deposition thereof on substrates, preferably composite substrates, and also all possible uses of this precursor solution. More particularly, the invention relates to a hybrid coating, which is impermeable and/or which has an omniphobic character, comprising at least two interpenetrated networks: the first being a silicic or aluminosilicic network, and the second being a polymer network; the two networks being bonded covalently or ionocovalently on the nanometer scale. The invention also relates to a process for treating the hybrid coating after deposition, preferably a heat treatment and/or UV irradiation treatment.