The serviceability of the sealing materials in a solar collector is of great importance. Extensive investigations have been carried out, mainly in the United States. They show that a large number of materials used has an ageing durability inadequate to the severe environmental conditions to which the collector is exposed. The materials used in Swedish made solar collectors are close to the best choice presented in these investigations. However, after accelerated ageing in laboratories for 26 weeks at 90 °C and 90 % relative humidity (RH), none of these materials fulfills all the important criteria in a satisfactory way. In most cases the compression set was too high. In the report is given a summary of the results of the investigations found in literature, and the results from the investigations carried out on sealing materials used in Swedish solar collectors.