Made with weather- and water-resistant glue, exterior plywood is designed to withstand wind, rain, and other weather conditions for many years. Exterior plywood is typically multi-ply for additional strength.
Exterior plywood is definitely harder to come by than exterior, and often only available in large quantities from specialist suppliers – the timber you buy at Bunnings for example, is almost definitely exterior grade. Clients often tell us that they have requested Exterior grade plywood and have unknowingly been sold exterior grade stock.