The SONODEC 25 GLX consist of a perforated aluminum inner duct, thermical insulated with a glass wool layer and provided with an aluminium laminated outer duct. An anti-migration barrier between the duct and the insulation wool adds strength and prevents the diffusion of insulation particles, as well as the following functions: improves acoustical performance, avoids cold bridges, leakage, pressure loss, protecting the R-value to be effected by humidity influences and avoid grow of fungus in the insulation wool. Both ends are taped to make ready-made connections.