Phenolic is highly compressed layers of paper. Ussually coated coated with something to help give it strength. I have never seen a phenolic spacer but I am willing to bet they coat them with some sort of epoxy type paint or resin to prevent the gas and heat from destroying it the first time out. I work in the woodworking industry and have worked with several different forms of phenolic. I am sure what I have worked with is a bit differrent but knowing how that stuff reacts to heat I dunno if I would be to willing to run it on my car.
