A process for the production of a heat-treatable low emissivity coated glass that comprises the steps of depositing an underlayer onto a glass substrate and subsequently depositing a reflective metal layer by a vacuum deposition process, wherein the underlayer is deposited by a pyrolytic deposition process. Preferably an anti-reflection layer is deposited by a vacuum deposition process on to the coated glass after deposition of the reflective metal layer. The underlayer may comprise a silicon oxide, the reflective metal layer may comprise silver and the anti-reflection layer may comprise a metal oxide, especially tin oxide or zinc oxide. The coated glass preferably has an emissivity of below 0.2 after heat treatment in an oxidising atmosphere.