Important COVID-19 Updates: ACCHaoS is not conducting school visits for the foreseeable future. Please check back for updates about when we will be scheduling events again.

Density Layers

Bottles filled with fluids of different densities
Some examples of our density layer bottles
Bottles filled with fluids of different densities
Some examples of our density layer bottles

A bottle is filled with fluids that float separately. You can add color to the fluids to make them more visible, and have floating items between the layers as well. You can tip the bottle gently and watch the layers stay separate.

This is a simple and fun creation that allows kids to express their creativity and learn about density.

Caution: Do not shake! It won't hurt it, but it will mix the layers and then you'll have to wait for the layers to separate again.


Density is the amount of mass per volume that a substance has. If one fluid has more mass than another fluid or object in the same volume, the denser fluid will sink while the less dense fluid or object will float. In this project, we use this fact to make our display bottles with separately layered fluids, and objects floating at different levels.

Salad dressing is often a mixture of vinegar and oil, which is why it will separate into layers if you leave it undisturbed for days or weeks. Natural peanut butter also separates, as the solids sink to the bottom and the oil floats on top. In both of those cases, you can shake or stir the layers to mix them again, but the effect is temporary, and eventually the layers will separate again.

You don't want to shake your display bottles, because then you will have to wait a long time for the oil and water to separate.


  • one or more small clear bottles or jars (plastic or glass is fine)
  • oil
  • water
  • food coloring
  • misc small items: cork, bits of brightly colored plastic, etc

Construction Instructions

Wash the bottles/jars well, and work over a sink, or outdoors, in case the water or oil spills.

If you're working with little kids, use plastic rather than glass. Peanut butter jars work well, if you can get them clean and clear. For older kids, jam jars or salsa jars are good.

Pour some water into the bottle, maybe 1/3 of the way full. Add food coloring, if you want.

Gently pour oil into the bottle, until it's about 2/3 full. You may want to tip the container and pour the oil onto the side of the container rather than onto the surface of the water, to preserve the layers. You can also pour the oil over the back of a spoon.

You can use mineral oil (sometimes called cutting board oil), or cooking oil, whatever you have on hand. Use something food-grade, so it's nontoxic if it spills. This can be a great use for an old bottle of stale olive oil, for example. Don't use coconut oil or other oil that can solidify at room temperature.

Decorate. You can cut a bottle cork in half and float that, or you can take some colorful bits of plastic packaging and cut them into confetti. Be creative, look around for things that float in water. If you can find things that float in water but sink in oil that's extra cool. Pick things that won't dissolve and are not organic (don't use paper).

You might want to duct tape or glue the cap/lid shut to avoid a mess if it opens. (Though we haven't, and for some reason kids never seem to try to open them.)