A controlled release product and a method for producing the controlled release product. The product includes a substrate material for release to a surrounding environment and a composition coating the substrate material in a coating layer for providing a controlled release of the substrate material. The composition includes a matrix material; a particulate fibrous filler material dispersed throughout the matrix material and a water soluble surface treatment material applied to the external surfaces of the particles of filler material such that the surface treatment material provides degradable interfaces between the matrix material and the external surfaces of the particles of filler material, and wherein the degradable interfaces are degradable in the presence of water such that interfacial passageways between the matrix material and the external surfaces of the particles of filler material are formed by the dissolution of the surface treatment material.