Abstract: Lightweight, structurally integral enclosures with walls stiffened and strengthened by integral and joined reinforcing ribs which may also serve as heat sinks. These ribs, which may be capped or uncapped and located on the inner or outer sides of the enclosure walls, are formed by chemical milling. Wall components are preferably joined by electron beam welding. Seals may be used between the walls and a closure to isolate the interior of the enclosure. In electronic applications, conductive seals and sealants are employed to provide uniform and continuous shielding from electromagnetic interference and radio frequency interference.