A method for producing a clad duct from a laminate comprising a rigid foam insulation panel (12) bonded to a sheet of thermoplastic material (14), said method comprising the steps of heating a portion of the sheet of thermoplastic material (14) in the vicinity of a first V-shaped groove (20) produced in the foam insulation panel until that portion of the sheet (14) becomes pliable, bending the sheet (14) where the sides of the first V-shaped groove (20) intersect until the V-shaped groove (20) closes, cooling the sheet (14) to or below a temperature at which the sheet retains its bent shape, repeating the heating, bending and cooling steps for a second V-shaped groove (20), and any additional V-shaped groove (20), and sealing a first edge (22) and a second edge (22) of the laminate. A special heat brake serves to heat the sheet of thermoplastic material.