Abstract: The present invention pertains to a process for manufacturing a solid composite layer, said process comprising the following steps: (i) providing a mixture comprising: at least one functional fluoropolymer comprising at least one hydroxyl group [polymer (F)], at least one metal compound of formula (I) [compound (M)]: X4-mAYm wherein X is a hydrocarbon group, optionally comprising one or more functional groups, m is an integer from 1 to 4, A is a metal selected from the group consisting of Si, Ti and Zr, and Y is a hydrolysable group selected from the group consisting of an alkoxy group, an acyloxy group and a hydroxyl group, and at least one inorganic filler material [filler (I)] in an amount of from 50% to 95% by weight, with respect to the total weight of said polymer (F) and said filler (I); (ii) reacting at least a fraction of said hydroxyl group(s) of at least one polymer (F) with at least a fraction of said hydrolysable group(s) Y of at least one compound (M), so as to provide a fluoropolymer com