An object with an internal cavity may serve as a cooling structure for a semiconductor package. The object includes a stack of form fitting bodies. The stack has a first form fitting body shaped according to the cavity with a first layer forming a partially form fitting surface, the first layer including a mixture of a first metal and an oxide of the first metal, and a second layer adjacent to the first layer. The second layer includes the first metal but less oxide of the first metal than the first layer. The stack has a second form fitting body shaped according to the cavity with a first layer forming a partially form fitting surface configured to conform to the partially form fitting surface of the first form fitting body.