The wood bricks are made compressed sawdust that is harvested from sawmills. I have used them several times, but they aren't ideal for my application. They burn TOO hot for my 1,200 square foot house, and they seem to burn and leave no coals. Also, make sure they stay dry. They are very absorbent! I had some stacked outside my front door, they got rained on and, even though they were still in plastic packaging, blew up like little life rafts.