Clouds will not form unless 3 “ingredients” are present:
2. Particulate matter
You’ll need an empty 2L plastic bottle with its cap, a match and a small scrap of paper.
Place several drops of water in the bottle - moisture. Use the match to light the small piece of paper on fire, let it burn for a few moments, then drop it into the bottle - particulate matter - and quickly cap it. Then apply pressure by squeezing the sides of the bottle. Release the sides and your cloud will appear. Squeeze again and the cloud will disappear. Release the sides and the cloud will reappear. You should be able to get the cloud to form several times before you need to begin again.
Encourage students to each bring in their own bottle, so they can each make their own cloud (the teacher should keep the matches). Also, you may want to encourage students to experiment to determine if it’s possible to form a cloud if one of the components is missing.