Rw is the ‘weighted sound reduction index.’ It is a number used to rate the effectiveness of the glass as a noise insulator and is measured in decibels (dB). It also takes into consideration a correction factor for the response of the human ear. For example, if a busy street has a noise level of 75dB and the required level of noise in a room is 40dB, the Rw value of the required glass is 35dB. Glass types with a Rw value greater than 35dB can then be offered as solutions.

It is worth remembering that every 10dB reduction is perceived by the ear as being half as loud, so that a 20dB noise reduction would reduce the perceived noise by 75%.