OSB (Oriented Strand Board) can get wet, but it's not waterproof and prolonged exposure to moisture can cause issues. While OSB can handle some rain during construction, it's best to minimize its exposure to water. If OSB gets wet, it can swell, particularly at the edges, and prolonged exposure can lead to warping, decay, and even delamination 

Plywood generally offers superior strength, stiffness, and moisture resistance compared to OSB, making it a better choice for structural applications where durability and longevity are paramount. While OSB is often more affordable, plywood's benefits often outweigh the cost difference, especially in demanding environments.