US Patent 8640264 Cap which utilizes an airfoil effect for inducing cooling

By adding a second smaller bill under the main bill of a cap and creating a gap from the front to the back between the two bills, the two bills create a curved shape that acts like an airfoil and allows the free flow of air over a wearer's forehead, inducing a cooling effect. Besides the benefit of a cooling effect, the appearance of the hat is such that an observer looking at someone wearing it would not be able to tell there was anything overtly different about the design.