Abstract: In order to reduce the heat transfer coefficient of coated building panels, the coating and the building panel have a high voidage. This high voidage can be obtained by using a fiber mat and a porous coating applied to the fiber mat. The porous coating includes porous glass particles and a low amount of a binder. The porous glass particles are held together by binder bridges, including a silicate binder and a low amount of an organic dispersion binder, for example an polymeric styrol acrylate. The partial volume filled by the binder bridges is small and therefore there is a remarkable first empty partial volume in between the porous particles. A second empty partial volume is located within the glass particles. The total volume of all pores of the glass particles is a relevant part of the total coating volume. This second empty partial volume is a very good thermal isolation because the individual pores are small and to a high percentage closed chambers not connected to the ambient.