We use a air bumper( about 4" OD) that slides in a brass tube.  The material that we have used for years is Micarta, which is basically wood.  We had a problem with water absorbation and the part swelling and jamming in the tube.  Could anyone recommend a material that would not swell when wet and have good thermal characteristics.  The environment can see about 80 C.  Teflon, I believe is too expensive and we tried a moly imprenated Nylon that deformed under heat.  Someone suggested puting varnish over the Micarta.  Could anyone suggest a material alternative to try.

thanks