Steel is often a recycled material, and as framing it is strong, lightweight and can go up fast. Steel is rot- and insect-proof and resists moisture damage. Exterior finishes and interior drywall can be attached with screws. Steel framing is fastened together, so it can be disassembled and reused. Steel members can degrade insulation R-values, however, so manufacturers have developed a variety of ways to reduce heat loss, such as cladding outside walls with foam board insulation.