As long as the Metseal seals and the cylinder bore surface are of the same material type or have the same or nearly the same coefficient of thermal expansion, the Metseal seal is very insensible to extreme temperatures. In hydraulic systems, it should be possible to operate with temperatures from -50 °C to +200 °C for standard material. In conjunction with special tempering of the standard material, an operating temperature up to +300 °C could be possible. The temperature limits should normally be established by the O-ring and not by the steel ring. The O-rings, which follow American standard, are readily available in most materials. As it is the Metseal seal in steel alone, that is responsible for the seal's prestress without compression set, the O-ring material can be allowed to have a compression setting. In seals made in soft polymeric material the material can be chemically affected by the pressure media. Apart from the risk that the seal material will expand, a lot of other changes, that can affect the properties of the material and jeopardize the seal's functions, can take place. Exchange of pressure media must be carried out with great precautions and will quite often call for a change of seal type or seal material to match the new media. In the Metseal piston seal, where the primary seal is made in hardened high-alloyed steel, the media can normally not affect the seal's material chemically. The O-ring is not responsible for the pre-stressing. The O-ring therefore has an easy task as a static seal and primary during the time when the primary seal change the contact side in the sealing groove, while the pressure direction is changed. For O-rings, that are following the American standard, one has the biggest choice of O-ring materials and that to a low cost. Practically and economically it is easy to select an O-ring material that can manage quite a number of divergent media, thanks to the fact that the functional demands for the material can be set low and relatively high swelling and settlement can be allowed.