Is usually defined “sound insulation” the ability of a window frame to act as a barrier to acoustic noise from the outside environment. The determination of the sound reduction is defined by the international standard ISO 140/3, and more generally by prEN 14351-1 - WI 00033279; in such regulations is provided the use of the double reverberation room for double glazing. During the test required to determine the sound insulation, the fixture is installed on the wall dividing two rooms acoustically isolated and normalized for size; to simulate the real behavior, in the chamber corresponding to the outer face the casing is installed a generator of pure tones, while in the chamber corresponding to the inner face is installed sound level meter. The difference between the acoustic intensity produced at different frequencies in the external chamber with the one measured inside defines the sound insulation in Db (A) (A decibel scale) of the frame in the test. On the basis of this result, the UNI 8204 provides for the classification of the frames into three categories (R1: 20 to 27 Db, R2: 28 to 35 Db, R3: more than 35 Db). According, then, to prEN 14351, & egrave possible to correlate empirically the minimum sound insulation for a window that has obtained at least a Class 3 air permeability, directly from the sound insulation of glazing used (and there & ograve as the predicted class 3 air permeability ensures experimentally a sealing of the perimeter parts of the closure, in this case represented by the seals, which do not interferes negatively on the insulation component of the glazing); thus, since & egrave prototypes tested fall into this condition (at least Class 3 perm. air), have a soundproofing power of not less than 34 dB, and therefore R2 class.