Rectangular ducts are made from galvanized or stainless steel. The sheets are cut and folded into the desired shape using automated machines controlled by computers for the highest precision. Moreover, customers can order the ducts to be sprayed with oil paint or powder color into the tone they wish. It can be lined with heat insulation both on the inside and on the outside, making it suitable for air duct and ventilation systems. All processes adhere to SMACNA and ASHRAE standards.