Cotton Ball Clouds

We are continuing our study of meteorology, and my student teacher did an activity with our students that I picked up at an NSTA area conference a couple of years ago. I think it’s a great way to help students visualize how much water a cloud really can hold. Of course, clouds aren’t really made of cotton balls, just a collection of water droplets!

So how many drops of water can a cotton ball hold? The answer may surprise you! (The original video I snapped of the process was over 5 minutes long, so I trimmed it down to just the end so you don’t get bored.)

I wish had done a better job with the follow up questioning. Ah well, something to work on for next time. In case you want to try this lab yourself, here are the materials and basic procedure. It’s really simple as you can see.


  • One cotton ball per student pair
  • One eye dropper per student pair
  • One beaker of water per pair or per table


  1. Give a cotton ball to each student pair.
  2. Have students predict how many drops of water they will be able to add to the cotton ball.
  3. Instruct one student to hold the cotton ball and the other student to add water to the cotton ball using the eye dropper – one drop at a time. Make sure to count each the drop.
  4. As you add drops to your cotton ball, you can move the cotton ball around so the entire cotton ball becomes saturated.
  5. Stop adding drops of water to the cotton ball when the cotton ball starts “raining.” Record number of drops added to the cotton ball.
  6. Discuss what this means about the amount of water in a cloud.

By Janelle

Space geek, science nerd extraordinaire. That's me! Want to know more, visit the About page.


  1. What a cool experiment. This actually raised more questions for me:, “if the cotton ball structure helps hold the water together – until saturation anyway – how do real clouds do it; what keeps the water droplets together? Does the shape/type of the cloud affect how much water is held or is it the other way around, does the amount of water held together dictate the shape?


    1. Those are some great questions, Malyn. I can answer some of it, but I’ll have to research some of the others.

      Cloud droplets are really small – much smaller than rain droplets, mist or drizzle. Also, in order for a cloud to form, the water needs something to condense onto – like dust or pollen in the atmosphere. The temperature of the air, pressure, humidity, and elevation when the could forms can also effect the size and shape of the cloud. Water is actually less dense than dry air, so that’s what keeps them all together until the cloud is so full it starts to rain.

      Clouds are really cool and amazing! Now I need to find out exactly what conditions create the different shaped clouds. I know they are associated with different air masses and fronts. I’ll see what I can find. The answers may come in another blog post!

      Thanks for stopping by!

    1. Thanks, Penny! I know when I first tried it out at the conference I attended it was amazing to see how many drops would fit in the cotton ball. The other great thing is it doesn’t take a lot of time or materials.

  2. Hi Janelle,

    It’s been raining a lot here lately and it reminded me of this post. I was thinking, if it works on saturation point, why doesn’t it stop raining? Is the saturation point for rain different for that to stop raining?

    Reading my question now – it doesn’t seem to make sense but hopefully you get me. Maybe another way of asking this is what makes raining stop?

    1. Hi, Malyn. I think a lot times when it continues to rain it’s because new clouds are continuous forming and moving in to the area. So one individual cloud might use up all of its rain, but another over full cloud moves in to take its place, and it keeps raining.

      Does that make sense?

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