Fire retardant plywood is specially treated with chemicals that act as a physical barrier to fire. The sheet material works by utilizing two mechanisms. One of them is reducing the flammability of fire-resistant plywood by lowering the rate at which flames travel and subsequently slowing down combustion.
The second mechanism involves the chemicals reducing the rate at which heat is released from the fire-treated plywood when there’s a fire. By altering the vapors released in the combustion process, it can make the flames less volatile.