A hydrolysable silane of the formula wherein each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; n = 1 to 3; Y represents an alkylene group having 2 to 6 carbon atoms; X represents -O- or -NH-; m = 0 or 1; R 1 represents a hydrocarbyl group having 1 to 8 carbon atoms; or R 1 represents a group of the formula -Y*-SiR q R" 3-q wherein Y* represents an alkylene group having 2 to 6 carbon atoms; each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; and q = 1 to 3; or R 1 represents a group of the formula wherein d = 1 to 8; R 8 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; R 9 represents a hydrocarbyl or substituted hydrocarbyl group having 1 to 20 carbon atoms; X" represents -O- or -NH-; m" = 0 or 1; Y** represents an alkylene group having 2 to 6 carbon atoms; each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; and r = 1 to 3; or R 1 represents a group of the formula -(CH 2) e -C OR 10 wherein e = 1 to 8; and R 10 represents a hydrocarbyl group having 1 to 8 carbon atoms; R 2 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; and R 3 represents a hydrocarbyl having 1 to 20 carbon atoms or where Z represents an oxygen atom and R 3 represents a group of the formula -((CH 2) a O) b -R 4 wherein a = 1 to 3; b = 1 to 6; and R 4 represents hydrogen or a hydrocarbyl group having 1 to 8 carbon atoms. wherein each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; n = 1 to 3; Y represents an alkylene group having 2 to 6 carbon atoms; X represents -O- or -NH-; m = 0 or 1; R 1 represents a hydrocarbyl group having 1 to 8 carbon atoms; or R 1 represents a group of the formula -Y*-SiR q R" 3-q wherein Y* represents an alkylene group having 2 to 6 carbon atoms; each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; and q = 1 to 3; or R 1 represents a group of the formula wherein d = 1 to 8; R 8 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; R 9 represents a hydrocarbyl or substituted hydrocarbyl group having 1 to 20 carbon atoms; X" represents -O- or -NH-; m" = 0 or 1; Y** represents an alkylene group having 2 to 6 carbon atoms; each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; and r = 1 to 3; or R 1 represents a group of the formula -(CH 2) e -C OR 10 wherein e = 1 to 8; and R 10 represents a hydrocarbyl group having 1 to 8 carbon atoms; R 2 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; and R 3 represents a hydrocarbyl having 1 to 20 carbon atoms or where Z represents an oxygen atom and R 3 represents a group of the formula -((CH 2) a O) b -R 4 wherein a = 1 to 3; b = 1 to 6; and R 4 represents hydrogen or a hydrocarbyl group having 1 to 8 carbon atoms. wherein d = 1 to 8; R 8 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; R 9 represents a hydrocarbyl or substituted hydrocarbyl group having 1 to 20 carbon atoms; X" represents -O- or -NH-; m" = 0 or 1; Y** represents an alkylene group having 2 to 6 carbon atoms; each R represents a hydrolysable group; each R" represents a hydrocarbyl group having 1 to 8 carbon atoms; and r = 1 to 3; or R 1 represents a group of the formula -(CH 2) e -C OR 10 wherein e = 1 to 8; and R 10 represents a hydrocarbyl group having 1 to 8 carbon atoms; R 2 represents hydrogen or a hydrocarbyl or substituted hydrocarbyl group having 1 to 8 carbon atoms; Z represents an oxygen or sulphur atom; and R 3 represents a hydrocarbyl having 1 to 20 carbon atoms or where Z represents an oxygen atom and R 3 represents a group of the formula -((CH 2) a O) b -R 4 wherein a = 1 to 3; b = 1 to 6; and R 4 represents hydrogen or a hydrocarbyl group having 1 to 8 carbon atoms.