The present invention relates to a solid active oxygen source coated with a composition comprising at least one polymer, wherein the composition on the oxygen source has been subjected to heating. Said oxygen source is chosen from percarbonates and said polymer is a hydrophobic alkyl cellulose, preferably ethyl cellulose. In a further aspect the present invention relates to a process for the production of a coated active oxygen source, wherein said oxygen source is in solid state and is formed into or in the shape of a granule, and wherein the coating is applied onto the oxygen source and subjected to heating by an application-drying process.
