Exposure 1 is a glue bond classification. It uses the same 100% waterproof glue as exterior panels and refers to a panel’s durability when long delays in construction are expected or when facing high moisture content. For plywood, see https://test.apawood-europe.org/products-trademarks/plywood/trademarks/glue-bond/. For OSB: https://test.apawood-europe.org/products-trademarks/osb/trademarks/exposure-durability-classification/
Structural 1 refers to a panel’s superior performance characteristics. For OSB, see https://test.apawood-europe.org/products-trademarks/osb/comparable-performance-requirements/
For Structural 1 plywood, all panels have special improved veneer grades and if manufactured to the US PS1 standard, the veneer grades will be species with a Group 1 strength classification. See group classification of species.