One reason for a reduced function in many solar collectors is that the covering plate is fogged by the volatile components in the sealing and insulation products. This so called outgassing also deteriorates the functions of the components. A rubber gasket e.g. hardens when the softener evaporates and the function of the sealing deteriorates. Several investigations of the outgassing tendency in solar collectors have been published. Many materials are unsuitable from the point of outgassing. A method for determination of outgassing has been developed within the scope of this project. The sealing and insulation materials used in solar collectors, made in Sweden, have been examined and investigated. The results show that outgassing from the products even happens at a temperature used by normal use. With a temperature corresponding to a stagnation situation, e.g. circulation failure, the quantity of volatile components is considerable.