This is the most popular question on the science.ca site and readers have pointed out it's probably for use in paintball. If that's what you want, go to www.google.com and type in: paintball smoke. You'll find a few websites where you can order such things for around $5 - $15.

Most home-made smoke bombs are a bit dangerous. As far as I know there is no "safe" smoke bomb. Many of the colours of pyrotechnics are made with toxic chemicals, so this would not be a good idea either

Image by: Freelance Illustration

Many readers have suggested the classic recipe of saltpeter (KNO3, potassium nitrate) and sugar, but this needs to be cooked and it can blow up while you heat it, so this is not recommended. One reader (a fifth form student in New Zealand) claims that you can make this kind of smoke bomb by mixing 3 parts KNO3 with 5 parts sugar, add a bit of powder from a firecracker or sparkler to get it started. Make sure you do this outside.

The other classic idea involves a ping-pong ball wrapped in aluminum foil but that also gives off somewhat toxic fumes as well as smoke.

Concerning the formula for making a smoke bomb, one chemist once said, "I tell kids if they can write down the instructions without using their hands, I'll give them the recipe."

Any search at www.google.com for "smoke bomb" will very quickly find a recipe for you. Main point: do it outside!!!