Nature Curtain is a cooling system designed for old buildings in the city. The purpose of Nature Curtain is to reduce CO2 emissions from air-conditioners. After special processing, sludge accumulated within dams can be fired and used to create a strong, lightweight, porous, water absorbent and heat insulating ceramic material. Nature Curtain utilizes the special characteristics of this material, and fixes this type of material to the exterior wall of buildings; thereby reducing the amount of sunlight the building itself is exposed to. This allows for the renewal of structures at minimum-cost.