A curtain is an outer cover of a building in which the outer walls non-structural. But merely keep out the weather as the curtain wall is non-structural.
It can be made of a lightweight material reducing construction cost, when glass is used as the curtainwall a great advantage is that natural light can penetrate deeper. Within the building and it is designed to resist air and water infiltration. The curtain wall faced does not carry any dead load weight from the building other than its own dead load weight. Curtain walls are typically designed with extruded aluminium members although the first curtain walls were made of steel. The aluminium frame is typically in filled with glass which provides an architecturally pleasing building as well as benefits such as daylighting. Other common in fills include: stone veneer metal panelling, louvers, and operable windows or vents.