b/c aluminum foil is in no way a to be used as a fire retardant its meant for food. you really need a reflector thats made of some actually semi decent metal. I would even try to have the reflector not even touch the wood so it doesn't conduct heat as well and there is only a layer of air that gets heated and not the metal to wood which is still prob dangerous. Wood would just absorb allot of you precious light. Get the most out of it by investing in something that will in your case make you grow safer and better. Gl and don't burn the house down.