The Kreditanstalt für Wiederaufbau (KfW) development bank supports the construction of energy-saving buildings. If a building has good thermal insulation, the windows may also be subsidised with funding from the KfW, if they make a positive contribution to the energy efficiency of the building. If they have a U value of 0.95 or less, up to 10 per cent of the purchase price of the windows can be reimbursed. The U value is a measure of the thermal insulation of components of a building, such as the windows. But this funding does not just apply to thermal insulation. Many federal states also provide KfW funding for soundproof windows. This is particularly the case for houses located near airports, which are exposed to particularly high noise pollution. If your building is in this type of location, it can definitely be worthwhile contacting the KfW when carrying out refurbishments or for a new build.