Round spiral ducts available in diameters from 80 to 1600mm from diameter 250mm they are provided with external corrugations to increase their stiffness and resistance to negative pressure. Although, as a standard, we sell air ducts made of galvanised steel sheet, we offer also ones made of copper, taking into consideration its antimicrobial benefits. Due to the fact that copper is known to suppress the growth of bacteria, fungi and molds, copper ductwork is a perfect solution for hospitals, schools, healthcare facilities like nursing homes and laboratories.