Anodized aluminium lacquered with polyvinylidene fluoride, anodized aluminium, vacuum evaporated aluminium foil and stainless steel have been aged up to 7 yr. It was found that anodized aluminium is not long-term durable, while the others show only slow deterioration. Stainless steel, however, has very low solar reflectance to make it useful. A promising material is lacquered aluminium, which is durable but tends to become scattering after ageing. Another promising reflector material is vacuum evaporated aluminium foil, which after more than 6 yr of ageing is still highly reflective and very specular. Light scattered within a cone of typically 20 degrees will hit the solar collector. Thus, the optical characterization should ideally be performed with scatterometers and integrating spheres with this acceptance angle. The characterization should, furthermore, be carried out at an incidence angle of 45 degrees for booster reflectors. The influence of the lacquering pre-deposition treatment on the optical properties has also been studied and it was found that a less aggressive process is beneficial for the optical properties.