When you're making a fire pit in your backyard or at your campsite, it can be helpful to recycle paper materials by burning them. Newspaper, leaves and untreated wood work well, as does uncoated cardboard. If you have a wealth of cardboard boxes lying around, feel free to use them for an outdoor fire. However, according to the University of Kentucky College of Agriculture's Burn Teaching Guide, you should never burn cardboard that is coated with a plastic-y residue, because this will release harmful chemicals into the atmosphere. Also, do not burn cardboard in your home, the Chimney Safety Institute of America warns, because this can lead to chimney fires that can compromise the structure of your chimney or start a house fire.
Use cardboard as kindling to start an outdoor fire. Cut or rip the cardboard into small strips and place it loosely in the fire pit, crisscrossing your strips. You can add newspaper as well if you wish. Place split logs crisscrossed in the fire venue and light the cardboard. Blow on it to keep it from going out.
Get rid of larger pieces of cardboard in an already burning fire by throwing manageable pieces onto the flames. Use a stick or poker to secure the cardboard in the fire so it does not blow away in the case of a wind gust.
Do not throw large pieces of cardboard on top of a fire because it will smother the fire and put it out. If you do want to burn a large piece of cardboard on a big, roaring fire, poke or rip holes in the cardboard so that oxygen can circulate.