Fabric Ducts are made of high-quality polyester fabric that is engineered for the specific requirements that are evenly distributed along the entire length of the duct through laser out precision air holes that ensure no hot or cold spots within the space. Fabric Ducts typically form part of a ventilation system that is used to convey air throughout a building. It is a simple elementary duct that is a fireplace chimney used to convey smoke to the outside.