A piston for a linear spool valve, the valve comprising a body having a inner surface. The body is made of a material with a relatively low heat expansion coefficient .alpha..sub.1. The piston comprises a contact member having an outer surface and being adapted to reciprocate within the body of the valve so that the outer surface is in contact with the inner surface. The contact member has at least a first layer made of a material with a heat expansion coefficient .alpha..sub.2 essentially greater than .alpha..sub.1, i.e. .alpha..sub.2>>.alpha..sub.1, and at least a second layer made of a material with a heat expansion coefficient .alpha..sub.3 close to .alpha..sub.1. This causes the contact member to be adapted to behave, along said outer surface, as a material having a heat expansion coefficient essentially closer to .alpha..sub.1 than to .alpha..sub.2. One of the layers constitutes an outer layer of the contact member and comprises the outer surface.