Clay is a fine-grained natural rock or soil material that combines different clay minerals with traces of metal oxides and organic matter. Depending on the content of the soil, clay can appear in various colors, from white to dull gray or brown to a deep orange-red. Clay can absorb humidity and transpire it as well.

Therefore it has a very positive effect on interior environments and ensures a healthy indoor climate. Similar to other materials clay stores heat with effect on isolation properties.