Activity Details



Use Orbeez (a small bead that expands when soaked in water) to explore topics like volume, density, statistical confidence, trend lines, inquiry science.


Orbeez, which illustrates growth  (a starter pack costs ~$7-10 US)


Challenge #1: Checking volume increase claims from various sources

Can you determine how many times bigger an Orbeez gets when soaked in water?
There's raging debate between parties disputing whether Orbeez can grow 100x or 150x growth when placed in water.
Challenge #2: Using Statistics to check volume increase claims
Find a creative way to determine your confidence that others will get similar results for actual growth. You can predict that you’re not going to get the exact same expansion factor every time. Consider these questions:
(0) When you checked the increase in volume the first time, was that right on average or was this one was an outlier? Was the claim of 100x or 150x an outlier? Why? How do you know?
(1) What’s the distribution of expansion factors?
(2) How can we use the resulting distribution to decide whether your first trial checking the volume increase was unusual or not?
Challenge #3: Attempt to predict the growth after only being allowed a short time before you must make your prediction.
How accurately can you predict how big the Orbeez will grow if you only have 60minutes to test before making a prediction? 120min? 24 hours?
How accurately can you predict how much time you will need for the Orbeez to grow to full size? 
Predict when the additional growth from soaking for longer time isn't worth the additional time. Pretend you are paid money for the largest Orbeez, but you must rent the facility where the Orbeez are soaked.
Challenge #4: Density prediction
Does the density of Orbeez change when they are soaked in water? Create and execute a procedure to show if it does. This should stand up under international scrutiny!
Challenge #5: Determine factors that dictate the potential size of Orbeez
Under what conditions can are the biggest Orbeez possible?  Big Orbeez are much more valuable to people. One person selling Orbeez soaks her Orbeez in diet soda and is making lots of money. What would you use?
Under what conditions are the most consistent Orbeez possible? One group needs a very precise Orbeez for some high tech applications - they MUST all be the same size. What do you need to do to produce Orbeez that are the same size, and are perfectly round?

Teacher Notes


Notes for Challenge #1:
Time consuming calculations of volume can be avoided when a simple comparison of the diameters using scale proportions is used. For example: if the large volume is really 150 times the small, then the large radius has to be at least 150^(1/3) = 5.3 times the small.
Another possibility to check accuracy:
Place a large number of them in a large graduated cylinder filled with (an excessive amount of) water. Video the expansion. Then you should be able to infer the (average) rate of expansion for one.
Notes for Challenge #5:
From Sharon Cohen, brand manager of Orbeez. (
"(100x growth) is after 5 hours of soaking, (150x growth) after a day and a half. They should reach 90x of full size after 4 hours, 100 percent after 8 hours."
Sharon also noted that the following liquids provide differences in final sizes, due to the ionic content of the liquid. (
"The disparity (150/100) is based on the fact that growth depends on ionic content of the water–the purer the water the larger they grow. The very same Orbeez wll grow to a different size depending on the water purity. The number we chose ended up being a marketing decision (100 is a powerful figure) but we should have been consistent. It's impossible to choose one accurate number."
"Smart Water 13mm; 13.45mm
Dasani 13.62mm; 13.45mm
Fiji 10.2mm; 11.85 mm
Market Pantry 13.3mm; 14.3mm
Arrowhead 9.4mm; 10.68mm
Aquafina 13.4mm; 13.96"


To preview and help understand Orbeez behavior



Time lapse of Orbeez growth (
Orbeez TV commercial (


This activity is directly drawn from the outstanding discussions taking place on Dan Meyer's blog (



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