A Thin Layer can be assigned different material models:

The first three material models are equivalent to the corresponding domain material, hence the discussion in Introduction to Material Models is valid also for thin layers.

The Spring Material is a special material model only available with the spring approximation. As the name implies, data for this material model is given in terms of spring constants, or as force as a function of extension. It can be useful for certain types of modeling where data is given in this format, for instance, when normal force versus closure curves are available.