A process of preparing a moulded article, the process comprising the following steps 1) hydrolysing a) at least one silane represented by formula RSiX 3, wherein R is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b) at least one compound selected from b1) a silane represented by formula R 2 SiX 2, wherein R, which may be the same or different, is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b2) a hydrolysable polysiloxane comprising non-hydrolysable organic groups, or a mixture thereof, and c) optionally at least one silane represented by formula SiX 4, wherein X, which may be the same or different, is a hydrolysable group, to prepare a composite composition comprising a hydrolysate or condensate of the hydrolysable components, wherein optionally nanoscale inorganic particles are added to the composite composition or a precursor thereof, 2) placing the composite composition in a mould, 3) curing the composite composition to increase the degree of condensation, 4) removing the moulded article from the mould, and 5) heat treating the moulded article at a temperature of at least 100°C, wherein at least one component in a gaseous state selected from water and an organic solvent is fed to the atmosphere under which the heat treatment of step 5) is carried out. 1) hydrolysing a) at least one silane represented by formula RSiX 3, wherein R is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b) at least one compound selected from b1) a silane represented by formula R 2 SiX 2, wherein R, which may be the same or different, is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b2) a hydrolysable polysiloxane comprising non-hydrolysable organic groups, or a mixture thereof, and c) optionally at least one silane represented by formula SiX 4, wherein X, which may be the same or different, is a hydrolysable group, to prepare a composite composition comprising a hydrolysate or condensate of the hydrolysable components, wherein optionally nanoscale inorganic particles are added to the composite composition or a precursor thereof, a) at least one silane represented by formula RSiX 3, wherein R is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b) at least one compound selected from b1) a silane represented by formula R 2 SiX 2, wherein R, which may be the same or different, is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b2) a hydrolysable polysiloxane comprising non-hydrolysable organic groups, or a mixture thereof, and b1) a silane represented by formula R 2 SiX 2, wherein R, which may be the same or different, is a non-hydrolysable organic group, and X, which may be the same or different, is a hydrolysable group, and b2) a hydrolysable polysiloxane comprising non-hydrolysable organic groups, or a mixture thereof, and c) optionally at least one silane represented by formula SiX 4, wherein X, which may be the same or different, is a hydrolysable group, to prepare a composite composition comprising a hydrolysate or condensate of the hydrolysable components, wherein optionally nanoscale inorganic particles are added to the composite composition or a precursor thereof, 2) placing the composite composition in a mould, 3) curing the composite composition to increase the degree of condensation, 4) removing the moulded article from the mould, and 5) heat treating the moulded article at a temperature of at least 100°C, wherein at least one component in a gaseous state selected from water and an organic solvent is fed to the atmosphere under which the heat treatment of step 5) is carried out.