According to an illustrative example of the invention, a gas spring comprises a cylinder and a piston rod. The piston rod is axially movable with respect to the cylinder and has a fastening eye mounted on the outer end of the piston rod. A tubular protection member surrounds an end portion of the cylinder adjacent to the end of the cylinder which is passed by the piston rod. The other end of the protection tube surrounds a holding disk fixed to the piston rod adjacent to the fastening eye. The protection tube and the piston rod define an air space therebetween. The air space is substantially tight against a liquid treating agent, such as a lacquer. On the other hand, the air space is in air flow connection with the surrounding atmosphere so that in response to axial movement of the piston rod with respect to the cylinder, excesssive pressure within the air space is prevented.