An on-line method of forming a multilayered coating on a sheet of fibrous or foam insulation, includes: applying a first coating layer of a first coating composition directly to a first major surface of the insulation sheet; heating an exposed major surface of the first coating layer to stabilize the coating composition at the exposed major surface of the first coating layer so that the first coating layer remains an essentially discrete layer when a second coating layer is applied to the exposed major surface of the first coating layer and to only partially cure the coating composition at the exposed major surface of the coating composition so that a second coating layer applied to the exposed major surface of the first coating layer will readily bond to the first coating layer; applying a second coating layer of a second coating composition directly to the exposed major surface of the first coating layer subsequent to heating the exposed major surface of the first coating layer; and heating the insulation sheet and the first and second coating layers, subsequent to the application of the second coating layer, until the first and second coating layers are substantially dried and cured.