Retrofitted secondary glazing provides an effective and sustainable way of improving the performance of a primary window. It can reduce heat loss and almost eliminate draughts, provide much needed acoustic insulation for those living and working in noisy areas, as well as providing varying levels of security for vulnerable windows and buildings deemed at risk. By improving U-values and reducing dB levels, it will increase the sense of well-being for users and make buildings more sustainable and comfortable to work and live in.