The surfaces of elastomeric coatings based on poly(dimethylsiloxane), unfilled or containing calcium carbonate filler or with filler and silicone oils, have been characterised from topographic and surface indentation measurements by atomic force microscopy. The resistance of the coatings to marine biofouling has been assessed in a sea-exposure trial, in which the strengths of attachment of some barnacles and tubeworms have been measured. In laboratory experiments, the materials have been challenged with oyster larvae (Crassotrea gigas), barnacle cyprids (Balanus amphitrite) and brown algal embryos (Sargassum muticum). Using a linear stress flow cell, the stresses required to detach settled larvae and embryos by fluid flow have been measured. The attachment of barnacles to the coatings was promoted by the microscopic surface roughness produced by protruding particles of filler. Oyster larvae and algal embryos were more readily displaced from surfaces that had been characterised as relatively soft, or from oil-bloomed surfaces.