Air-conditioning duct

An air-conditioning duct for vehicles comprising:

• a first duct formed by incorporating in parallel a first polygonal unit duct with a flange formed around an opening periphery thereof and a second polygonal unit duct with a flange formed around an opening periphery thereof;
• and
• a second duct mutually connected to the first duct, the second duct being formed by incorporating in parallel a third polygonal unit duct with a flange formed around an opening periphery thereof and a fourth polygonal unit duct with a flange formed around an opening periphery thereof,
• wherein the first duct and second duct are connected in series with one another, the flange formed on a boundary side of the first polygonal unit duct and the flange formed on a boundary side of the second polygonal unit duct overlap and are fixed with one another, the flange formed on a boundary side of the third polygonal unit duct and the flange formed on a boundary side of the fourth polygonal unit duct overlap and are fixed with one another, the openings of the first unit duct and the second unit duct are formed in an inclined manner with respect to the longitudinal direction of the first and second unit ducts, the openings of the third unit duct and the fourth unit duct are formed in an inclined manner with respect to the longitudinal direction of the second and third unit ducts and the flanges of each of the unit ducts are inclined at the same angle as the openings of the unit ducts, the flange formed on the boundary side of the first unit duct is an outer flange, the flange formed on the boundary side of the second unit duct is an inner flange, the flange formed on the boundary side of the third unit duct is an outer flange, the flange formed on the boundary side of the fourth unit duct is an inner flange, a cross-section area of the first unit duct is larger than that of the second unit duct, a cross-section area of the third unit duct is larger than that of the fourth unit duct and, when connecting the first duct with the second duct, the first unit duct and the third unit duct are connected and the second unit duct and the fourth unit duct are connected.