Novel fluoroalkysilanes of the following formula are described; Rf—O—CHFCF2—O—(CH2)n—Si(R)xX3−x, wherein Rf is a perfluoroalkyl group, optionally substituted by one or more in-chain -Q-, —S— or —NRf1-heteroatoms, where Rf1 is a -perfluoroalkyl; X is a hydrolysable group; R is a C1C4 alkyl group; n is at least 3; and x is 1 to 3.