Hard fabric is a thermo-hardening plastic

Hard fabric is a thermo-hardening plastic, made of layers of cotton fabric soaked in phenol resin, which is compressed under high pressure. It is a relatively inexpensive plastic, which can be used up to about 120˚C and thereby retains its good mechanical properties.

It is an excellent electrical insulator, has great stiffness and hardness and with a low expansion co-efficient possesses good measurement retention at high temperatures