Not as much as you might think. Standard double glazing has quite a small air gap between the two glasses which limits the effectiveness. The maximum gap for a sealed double glazed unit is about 22mm which will make some difference. However, the use of an air gap of 50mm to 200mm will make a substantial difference. This cannot be achieved with standard sealed double glazing. It would require two window frames set one behind the other to create the gap. VLam Hush™ used in either one pane or both is ideal where you need noise protection along with thermal comfort.