Fibreboard composition, [or 'compo' as it was known], is a pressed resin/woodfibre material of immense strength when dry. It far outperforms crummy plastic grips- just try breaking a piece with your fingers!
It was much used in the pre-plastic era for electrical insulation in transformers, switchgear and motors.
One modern use is for seals in domestic water connections here in France, because it swells when wetted, effecting a reliable joint.
Historical note: The British Army issued our squaddies with 'compo' ID dog-tags during WW2 for economy. The poor blighters who fell on the Normandy beaches became unidentifiable when the tags disintegrated in the seawater.
Alan
