Grow a Rainbow Science Experiment

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This colorful grow a rainbow science experiment is truly magical! Kids will love to watch the rainbow grow in this easy STEM activity that you only need paper towels, water, and washable markers for.
How to grow a rainbow science experiment

If you’re looking for a simple but cool science experiment that doesn’t require a lot of supplies, then you’ve come to the right place!

All you need to grow your own rainbow is a paper towel, washable markers, and water.

Although I can’t promise that you’ll find a treasure at the end of this rainbow, I can guarantee that your kids will love seeing the rainbow magically come together in this simple science experiment!


Supplies Needed for Grow a Rainbow Science Experiment

This pom-pom sorting activity requires almost no prep and will keep your toddler or preschooler concentrated in some educational sensory play! 


Watch the Full Video Tutorial Here




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How to Grow a Rainbow 

1. Fold the paper towel in half and cut off about 1/3 of the paper towel.

2. Draw rectangles of the rainbow colors on each end. Make sure to go over the colors a few times with the markers so there is enough dye to travel up the paper towel.

Grow a rainbow experiment

How to Grow a rainbow experiment


3. Pour water into the two glasses until they are about 3/4 full.

4. Place the paper towel into the cups, with one end in each cup. Make sure that the ends aren’t too deep in the water or the dye may dissolve into the water instead of moving up the paper towel.

How to Grow a rainbow science experiment

You’ve successfully planted a rainbow! Now it’s time to watch how the rainbow grows as the colors travel up the paper towel! 

How to grow a rainbow at home


The Science Behind the Paper Towel Rainbow Experiment

To put it simply, capillary action makes the water and dye move up the paper towel.

The water adheres to the walls of the small vessels in the paper towel, causing an upward force on the liquid at the edge. In simpler terms, capillary action allows liquid to move through or along the surface of another material (the wall) in spite of other forces such as gravity. As the water moves upward through the paper towel, it’s lifting the washable dye molecules with it.

Because we use water-based washable markers in this experiment, they disperse in water. If you were to try this experiment with permanent markers it wouldn’t work because the markers are alcohol-based and not water-based so the dye in the marker can’t travel with the water.

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Other examples of capillary action:

  • When you dry yourself with a towel after a shower, the towel absorbs the water from your body by using capillary action.
  • The tear duct in the corner of each eye is a narrow tube that uses capillary action for drain excess tears into the nasal passage.
  • Plants and trees use capillary action to live. Water is absorbed by the roots, and capillary action allows the water to travel up the plant. This is why we should water the soil near the roots of our plants instead of the leaves.


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