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The box's fenders and outer tailgate panel are made of reinforced reaction injection molded (RRIM) materials, chiefly polyurea with mica filler. The one-piece inner panel and the inside of the tailgate are formed by a structural reaction injection molding (SRIM) process and consist of a 50/50 mix of urethane and glass fiber. The interior of the box and tailgate are painted with a dark gray "spatter paint" that provides a tough, pebbly surface as well as protection from ultraviolet rays.
The use of composite materials reduces the total weight of the truck by approximately 50 lbs., which improves fuel economy and payload carrying capability. The tailgate alone is 15 lbs. lighter than a current steel tailgate.