A tool and a method for forming a tool are disclosed. The tool has a base layer additively formed from a polymer material in a desired tool shape. In addition, a sealant layer is formed over an outer surface the base layer. The sealant is a low-modulus material such as a silicone rubber or an elastomer. In one embodiment, the sealant is made electrically conductive by the addition of a filler to the low-modulus material. The filler material may be one of carbon black, carbon fibers, graphene, carbon nanotubes, and metallic whiskers, for example. In another embodiment, the sealant is not electrically conductive and an electrically conductive layer is formed over the sealant layer. Finally, a metallic coating, preferably multilayer, is formed over the sealant layer by electroplating or electrodeposition.