A wood stove baffle is a section of heavy-gauge metal installed inside the firebox just below the stove's top. It deflects the heat from coming into direct contact with the top of the stove.
Baffles create a barrier between the fire and the top of the wood stove, as well as a path for the smoke and gases to follow toward the stovepipe. They also reflect the heat back toward the fire, causing a secondary combustion during which most of the gases are burned off, resulting in an efficient burn, and they prevent smoke from blowing back out of the stove when the door is opened.
Some stoves are equipped with a fireproof ceramic blanket that's positioned between the baffle and the top of the firebox. Fibers in the ceramic blanket may release particles that should not be inhaled, according to the Wood Heat Organization.
Baffles are made of steel, cast iron, firebrick, ceramic fiber board, or a combination of these, according to the Wood Heat Organization. Because they're exposed to such intense heat, they must eventually be replaced. Instructions for doing this are included in the stove's owner's manual, and parts can be purchased from stove dealers or manufacturers.