Aside of sintered PTFE, gold coatings are another possibility to obtain a diffuse, ideal Lambertian reflectance in the infrared area. With a reflectance value of more than 95% from 800nm to 5000nm InfraGold® is used for integrating spheres and their components. The cold coating is applied galvanically onto aluminum- or brass surfaces. Thermal stability up to 1000°C und long life are convincing arguments for such a capital spending. The gold coating is chemically inert and not susceptible for dirt, but should be treated as other optical components.