Another possibility is the Phenolic resin based material manufactured under the trade name “Tufnol” it is made in several grades and thickness, the thinner sheets are used for circuit boards, the type reinforced by layers of linen, it used to be called “carp brand” would probably be favourite. A similar sheet material made from GRP is also available but is more aggressive on cutting tools. The obvious sources for such materials would be the likes of Radio Spares or Maplin Electronics.
