A composite building material, comprising: a core layer comprising a first type of polymeric fibers and a first binding agent, the first type of polymeric fibers having a first average fiber length; a top layer disposed above the core layer and comprising a second type of polymeric fibers and a second binding agent, the second type of polymeric fibers having a second average fiber length different than the first average fiber length, wherein the second average fiber length is less than the first average fiber length, so that an average length of polymeric fibers in the core layer is greater than an average length of polymeric fibers in the top layer; an optional bottom layer disposed below the core layer and comprising the second type of polymeric fibers and the second binding agent, wherein an average length of polymeric fibers in the core layer is greater than an average length of polymeric fibers in the optional bottom layer; and at least one surface layer of resin-impregnated paper disposed above the top layer or below the optional bottom layer, wherein the first type of polymeric fibers and the second type of polymeric fibers are compressed, wherein at least one of the first type of polymeric fibers or the second type of polymeric fibers comprises fibers derived from at least one of a scrap fiber source, a used fiber source, a recycled fiber source, or any combination thereof, wherein the first binding agent and the second binding agent are derived from Methylene diphenyl diisocyanate and comprise at least one of a polyurea or a polyurethane, wherein the core layer comprises a substantially nonuniform thickness, and the core layer, the top layer, and the optional bottom layer together comprise a substantially uniform thickness, and wherein the core layer, the top layer, the optional bottom layer, and the at least one surface layer form a board or a sheet. a core layer comprising a first type of polymeric fibers and a first binding agent, the first type of polymeric fibers having a first average fiber length; a top layer disposed above the core layer and comprising a second type of polymeric fibers and a second binding agent, the second type of polymeric fibers having a second average fiber length different than the first average fiber length, wherein the second average fiber length is less than the first average fiber length, so that an average length of polymeric fibers in the core layer is greater than an average length of polymeric fibers in the top layer; an optional bottom layer disposed below the core layer and comprising the second type of polymeric fibers and the second binding agent, wherein an average length of polymeric fibers in the core layer is greater than an average length of polymeric fibers in the optional bottom layer; and at least one surface layer of resin-impregnated paper disposed above the top layer or below the optional bottom layer, wherein the first type of polymeric fibers and the second type of polymeric fibers are compressed, wherein at least one of the first type of polymeric fibers or the second type of polymeric fibers comprises fibers derived from at least one of a scrap fiber source, a used fiber source, a recycled fiber source, or any combination thereof, wherein the first binding agent and the second binding agent are derived from Methylene diphenyl diisocyanate and comprise at least one of a polyurea or a polyurethane, wherein the core layer comprises a substantially nonuniform thickness, and the core layer, the top layer, and the optional bottom layer together comprise a substantially uniform thickness, and wherein the core layer, the top layer, the optional bottom layer, and the at least one surface layer form a board or a sheet.