Simulated stone, masonry and brick textured products such as siding panels are obtained when specially selected materials are properly admixed and formed via molding techniques. For instance, exemplary methods of manufacturing embodiments of panels, wall structures, and other products that may have contoured and textured surfaces and may simulate the appearances of conventional building or construction materials including, but not limited to, stone, bricks, masonry, concrete, stucco, wood, other conventional building materials, and combinations of any of these materials are disclosed. Such products are manufactured from suitable molds according to a prescribed process methodology using synthetic polymeric materials in addition to other materials such as coloring and texturing materials. Prerequisite surface textures may be produced that effectively simulate actual stone, masonry and brick panels. Methods described herein may enhance the manufacturing, structure, appearance, assembly, or installation of synthetic building or construction products. In particular, exemplary embodiments include panels, wall structures, and other panel assemblies that may have contoured or textured surfaces to simulate the appearances of other building or construction products. The disclosed invention is not limited to products in the building or construction industries and may be applied in the manufacture of a wide variety of products in other industries.