Phenolic paper
Phenolic paper is a paper [composite panels|paper composite] material often used to make printed [circuit board|printed circuit board (PCB)] substrates. It is a very tough board made of wood fibre and Phenol [formaldehyde resin|phenolic polymers]. It is most commonly brown in colour, and is a fibre reinforced plastic. These PCB materials are known as FR-1 and FR-2 – FR-2 is rated to 130°C, FR-1 is rated to 105°C.