Currently, most code authorities accept the functional equivalence of plywood and OSB structural panels. This position is promoted strongly by trade groups within the “engineered wood” industry. At the same time, most construction professionals who work with the two products assert exterior plywood tends to better survive extended moisture exposure than does a comparable OSB panel. Testing confirms that OSB has a somewhat greater resistance to moisture infiltration and a somewhat greater resistance to exfiltration of moisture within the panel, and it is this tendency of OSB to retain excess moisture that can foster mold growth and wood decay. Such differences in “moisture exchange” performance should not be considered a deficiency in the OSB product. When properly installed, neither OSB nor plywood should be exposed to moisture extremes; however, design/construction teams must look beyond the industry’s existing structural performance rating system to evaluate project-specific risk factors that may favor the specification of plywood.