Tubo de ar fresco

with 102 mm inner diameter and 110 cm length. Construction: inner and outer layer of bitumen paper interleaved with single layer of aluminium, external colour: black kraft paper, temperature upto 100°C

Pliable ducting manufacured by winding strip steel, aluminium or other malleable maerials together in various combinations. Basically, one, two or three layers of strip are spirally wound round a cylindrical mandrel with an overlap of each layer. Convolutions are then rolled into packed layers proving strength but, at the same time, permitting bending without bore distortion.
The type of dusting requiered varies with application.
Sometimes the lightweight construction of paper/aluminium is sufficient for warm air ducts in the automotive industry. Alternatively the use of lacquered aluminiums increase performance and improves appearance. For heavy duties, layers of steel and aluminium may be necessary for greater strength. Standard grades have good heat and acoustic insulation properties and are pliable, retaining their curvature without springing back.
Long lengths may need supporting with suitable clips.