Bakelite, phenolic plastic, teflon, acrylic, or maple are good materials to make carb spacers out of. They can all take the heat of the intake manifold just fine. I wouldn't use aluminum because the whole point of the spacer is to keep the carb from getting heat from the manifold. I wouldn't use asbestos because of the health hazard. It may also decide to flake and ruin your engine.
