A method of forming a linear panel having a linear panel shape comprising a body including a panel wall and first and second sidewalls (54, 56) extending outwardly from the panel wall, each of the first and second sidewalls (54, 56) being bent at an edge portion (58, 60) of the body to form respective first and second flanges (62, 64), the method comprising: heating an inner material layer to a processing temperature at or above its melting temperature to allow an outer material layer to be adhered to the inner material layer to form a multi-layer panel material assembly comprising the inner material layer and the outer material layer, the inner material layer differing from the outer material layer; drawing the panel material assembly along a processing path; heating the panel material assembly to a processing temperature as the panel material assembly is drawn along the processing path, the processing temperature being greater than a forming temperature of the inner material layer and less than a forming temperature of the outer material layer; forming the heated panel material assembly into the linear panel shape; and cooling the panel material assembly after it has been formed into the linear panel shape and as the panel material assembly is drawn along the processing path, wherein the material properties of the outer material layer are selected such that the outer material layer is flexible enough at the processing temperature used during forming to allow the outer layer to follow the shape of the inner material layer as the inner material layer is being formed into the linear panel shape; and, in the formed linear panel, the inner material layer and outer material layer are separate material layers, the inner material layer defining an inner surface of the body, and the outer material layer defining an outer surface of the body. heating an inner material layer to a processing temperature at or above its melting temperature to allow an outer material layer to be adhered to the inner material layer to form a multi-layer panel material assembly comprising the inner material layer and the outer material layer, the inner material layer differing from the outer material layer; drawing the panel material assembly along a processing path; heating the panel material assembly to a processing temperature as the panel material assembly is drawn along the processing path, the processing temperature being greater than a forming temperature of the inner material layer and less than a forming temperature of the outer material layer; forming the heated panel material assembly into the linear panel shape; and cooling the panel material assembly after it has been formed into the linear panel shape and as the panel material assembly is drawn along the processing path, wherein the material properties of the outer material layer are selected such that the outer material layer is flexible enough at the processing temperature used during forming to allow the outer layer to follow the shape of the inner material layer as the inner material layer is being formed into the linear panel shape; and, in the formed linear panel, the inner material layer and outer material layer are separate material layers, the inner material layer defining an inner surface of the body, and the outer material layer defining an outer surface of the body.