What is the difference between compositional and structural layers?

Compositional layers refer to the distinct materials that make up a planet, such as the crust, mantle, and core, each defined by their chemical composition. In contrast, structural layers are defined by their physical properties and behavior, such as lithosphere, asthenosphere, and mesosphere, which are characterized by their rigidity or fluidity. While compositional layers focus on what materials are present, structural layers emphasize how those materials interact and behave under different conditions.