In reply to Rampart:
> Swinging a tool into Celotex feels quite a lot like neve. Not sure I'd want to trust weight to it, though.
Waiting for a teabag to brew, I have just buried an old MT vertige into some 50mm Celotex.
Flick of wrist to get 50mm in.
Pulling up on it, Celotex on shelf, it ripped through at about 15kg.
Heavier grades available, trip to local builders supply maybe, try explaining why you want to bury an axe into every sheet on their shelves, could be an expensive day out!