What material is affected by exposure to direct sunlight, leading to warping or cupping?

Plywood is the correct material that can be affected by exposure to direct sunlight, leading to warping or cupping. This is primarily due to its composition, which consists of multiple layers of wood veneers glued together. When exposed to sunlight, especially in areas with fluctuating temperatures, the outer layers of the plywood can expand and contract at different rates compared to the inner layers. This differential movement can cause the plywood to warp or develop a cupped shape.

In contrast, metal typically has a high resistance to warping and is less susceptible to changes from sunlight exposure. Plastic can also degrade or discolor under harsh sunlight, but it does not generally warp in the same manner as plywood. Glass is rigid and stable, remaining unaffected by sunlight in terms of structural integrity. Therefore, plywood is uniquely vulnerable to the physical changes brought on by sun exposure, making it the material that is most likely to experience warping or cupping as a result.