A method for depositing a protective coating onto a substrate, wherein: the protective coating comprises (i) a moisture-barrier layer which is in contact with the substrate and which comprises a first sub-layer, optionally one or more intermediate sub-layers, and a final sub-layer, (ii) a mechanical-protective layer which is inorganic, and (iii) a gradient layer interposing the moisture-barrier layer and the mechanical-protective layer; and the method comprises: (a) depositing the first sub-layer of the moisture-barrier layer onto the substrate by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; wherein: Z 1 represents C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 2 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 3 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 4 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 5 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; and Z 6 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl, (b) depositing, when present, the one or more intermediate sub-layers of the moisture-barrier, each by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; and (c) depositing the final sub-layer of the moisture barrier layer by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; characterised in that the method further comprises: (d) depositing the gradient-layer onto the final sub-layer of the moisture-barrier layer by plasma-deposition of a precursor mixture which comprises the components of both precursor mixtures and; and (e) depositing the mechanical-protective layer onto the gradient-layer by plasma-deposition of a precursor mixture comprising an organosilicon compound. the protective coating comprises (i) a moisture-barrier layer which is in contact with the substrate and which comprises a first sub-layer, optionally one or more intermediate sub-layers, and a final sub-layer, (ii) a mechanical-protective layer which is inorganic, and (iii) a gradient layer interposing the moisture-barrier layer and the mechanical-protective layer; and the method comprises: (a) depositing the first sub-layer of the moisture-barrier layer onto the substrate by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; wherein: Z 1 represents C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 2 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 3 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 4 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 5 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; and Z 6 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl, (b) depositing, when present, the one or more intermediate sub-layers of the moisture-barrier, each by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; and (c) depositing the final sub-layer of the moisture barrier layer by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; (a) depositing the first sub-layer of the moisture-barrier layer onto the substrate by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; wherein: Z 1 represents C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 2 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 3 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 4 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 5 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; and Z 6 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl, Z 1 represents C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 2 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 3 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 4 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; Z 5 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; and Z 6 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl, (b) depositing, when present, the one or more intermediate sub-layers of the moisture-barrier, each by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; and (c) depositing the final sub-layer of the moisture barrier layer by plasma-deposition of a precursor mixture comprising an organosilicon compound, a fluorohydrocarbon or a compound of formula; (d) depositing the gradient-layer onto the final sub-layer of the moisture-barrier layer by plasma-deposition of a precursor mixture which comprises the components of both precursor mixtures and; and (e) depositing the mechanical-protective layer onto the gradient-layer by plasma-deposition of a precursor mixture comprising an organosilicon compound.