Disclosed herein is a siding member for covering an exterior of a structure. The siding member comprises a siding panel having a nail hem and a rear face, wherein the rear face is generally shaped to provide a receptacle capable of retaining a liquid material. In addition, the siding member includes an extension located at an upper edge of the siding panel and a channel located at a lower edge of the siding panel. The channel is of a shape and size to receive the extension of an adjacent panel. A stiffening material is poured or sprayed into the receptacle generally filling the receptacle.