Sugar Rainbow Density | Science Experiment

Sugar Rainbow Density Science Experiment

Get a colorful lesson in food science with our Sugar Rainbow Density Science Experiment, where density differences are revealed in a colorful stack of sugar-water samples.
Understanding density has never been easier — or more colorful — than with our rainbow density experiment. The Sugar Rainbow is a creative and engaging way to see how liquids of different densities stack on top each other. (Hint: There’s an additional lesson about adhesion and cohesion in the mix for you, too.) A simple combination of some everyday table sugar and vibrant colored water leads to an awesome science experience about density. Ready for it? Let’s go!

Experiment Materials

    No Products

  • 6 Tall, clear glasses (See NOTE in Step1.)
  • Granulated sugar (You’ll have great results with Imperial Sugar or Dixie Crystals.)
  • Coloring tablets or food coloring
  • Water (See NOTE in Step 3.)
  • Clear drinking straw
  • Measuring spoons
  • Small dish or sink
  • Adult supervision

Experiment Videos



Fill each of the six glasses with water. NOTE: The glasses need to be stable and about as deep as the straw is long. As you fill the straw with solutions, it has to be plunged deeper and deeper into the liquids.


Use coloring tablets or food coloring to dye the water a different, bright color in each glass. Stir it completely.


The first of the six glasses will be just colored water with no sugar. The second color receives one rounded teaspoon of sugar. The third color receives two rounded teaspoons of sugar. The fourth gets three teaspoons and so on to five teaspoons of sugar in the last glass. Stir the solution in each glass until the sugar is completely dissolved. NOTE: Using warm or room temperature water will speed up this process.


Grab the straw and, if you haven’t already, remove the wrapper. Hold the straw near one end, wrapping four fingers around the straw and placing your thumb over the straw’s top opening. To make your Sugar Rainbow, lift your thumb off the opening, dunk the lower end of the straw about 1” (3 cm) into the plain water. Cap the straw firmly with your thumb, lift it out of the water, and dip it quickly into the 1 tsp solution. This time, go a little deeper than you did into the first glass. You want the layers to be about the same thickness. With the straw in the liquid, lift your thumb but quickly replace it. Lift the straw and you’ll have the first and second colored solutions in a stack inside the straw. Continue the dipping process until you have all six colored solutions inside the straw. It’s a density column of sugar water, a Sugar Rainbow!

When you’re ready, hold the straw over the dish and lift your thumb to empty the straw. Rinse it and make another one.

How Does It Work

What exactly is “density?” Well, density is the measurement of how much “stuff” is packed into a measured space. That’s how we get the equation for density: Density = Mass (the stuff) ÷ Volume (a measured space). Nearly every substance and material imaginable has a different density. This is especially true for those six colorful solutions you made using sugar and water.
By increasing the amount of sugar in the solution (but keeping the amount of water constant), you created solutions that have increasing densities. The more sugar that was mixed into a measured amount of water, the higher the mixture’s density became. As the Sugar Rainbow’s density was revealed, the solution with the lowest density stacked on top of a mixture with a higher density.
So, density explains why the solutions stacked on top of each other inside the straw. However, what kept those solutions inside the straw? Wouldn’t they just pour out of the straw as you lifted the straw from the solution? That’s where our bonus lesson in cohesion (similar molecules attracting each other) and adhesion (different molecules attracting each other) came into play. A surface tension sealed the water at the bottom of the straw. That surface tension was strong enough to help hold the solutions inside that straw — as long as air pressure inside the straw was lower than the air pressure outside of the straw. Gravity tugged those sugar-water solutions downward, which created a slight vacuum in the empty part of the straw. That lowered the air pressure inside the straw, which is why you needed your thumb to cap the straw. Your thumb prevented air pressure from equalizing inside the straw.
The second you remove your thumb, air pressure equalizes and then gravity simply moves the colored solutions out.

Take It Further

Instead of a straw, use a turkey baster as a replacement for an even larger scale experiment on our rainbow water density experiment. Slowly layer the colored sugar solutions into a larger glass to create an even bigger rainbow! Hold the tip of the baster against the side of the container close to the surface of the liquid already in the glass. Squeeze the baster gently so the water flows slowly down the side of the container and then onto the previous layer. But take your time: if you try to rush it, the layers will just mix together. Rinse the baster between each layer. Move the baster upward on the side of the glass, as needed, so it doesn’t touch the surface of the solution. Layer all the sugar solutions in the same way. This can be hard to do but it’s worth the effort when you finish. Get some pictures!

Fun Fact

A dramatic saltwater density change can be experienced in real life. While humans will (sort of) float in an ocean, they will REALLY float in bodies of salt-saturated water, like Utah’s Great Salt Lake and the Dead Sea in Israel and the West Bank. They are so salty that it’s nearly impossible to sink in them! (Just be sure to rinse off really, really well when you get out.)

Rainbow Density Science Experiment

Although making colorful layers of water is a cool trick, it isn’t necessarily a science experiment. To make this into a science experiment, you’ll need to introduce a variable, while you’re keeping other things the same. Some variables may include the temperature of the water (warm, room temperature or cold) or the type of sugar that you mix into the water (turbinado sugar, white sugar, confectioner’s sugar or artificial sugar).

Rainbow Experiments with Water — and More

In our rainbow experiment with water, sugar and food coloring, you were able to see some everyday scientific principles firsthand. There’s more where that came from! Don’t miss our other hands-on scientific experiments (like our rainbow density experiment) that will amaze your friends and impress your family with your scientific knowledge. Just about all of our science experiments for kids use ordinary ingredients that are easily found in your home or kitchen to create some extraordinary, memorable effects. From food science and color science to more density and forces and motion experiments, there are fun experiments for kids that will inspire kids to ask questions and be inquisitive about science.