Abstract: The invention provides an anodised aluminium product for use in a metal core printed circuit board which in which the anodised layer forms a dielectric, and the resultant metal core printed circuit board has a sandwich structure having a thermal conductivity higher than and a thermal resistance lower than conventional metal core printed circuit boards using alternative dielectric layers, and with improved electrical insulation properties. The invention has application in manufacture of rigid and flexible printed circuit boards which have a metal substrate, manufacture of a heat conductive substrate for semiconductor devices, and electronic devices. While the use of the invention is described in relation to metal core printed circuit boards, the anodising process and anodised aluminium of the invention may have other applications beyond this technology. The invention also provides a method of manufacturing such an anodised aluminium product.