Abstract: A seal arrangement, for example a brush seal 8? in a gas turbine engine, includes thermal matching means for matching the rates of response of a supporting ring 14?, 16? of the seal, and of a rotatable component 4 with which the seal cooperates, to thermal changes in the environment of the seal induced by changes in operating conditions. The thermal matching means may comprise a slugging mass 24 and/or thermal insulation 28. Alternatively, or in addition, the region 24 of the housing at which the seal 8? is mounted may be made from a relatively low thermal expansion material. These measures reduce the rate of expansion and contraction of the seal 8? as the temperature in the engine varies so as to match more closely the rate of expansion and contraction of a rotatable component with which the seal cooperates.