Museum of Science, Boston

Books for Kids

  • Snow Crystals
    , by
    W.A. Bentley and W.J. Humphreys
  • Snowflake Bentley
    , by
    Jacqueline Briggs
  • The Magic School Bus Lost in the Snow
    , by
    Joanna Cole
  • The Snowflake: Winter’s Secret Beauty
    , by
    Ken Libbrecht

Contact Us

Contact the Discovery Center and Living Lab staff at

January 2012: Capillary Action Snowflakes

Capillary Action Snowflakes

Young children love to explore water! And no wonder- playing in water, with all of it’s interesting properties, presents young children with both satisfaction and challenges. The Capillary Action Snowflakes activity allows children to explore one of water’s most appealing properties: it’s “stickiness”. Water molecules stick to almost everything- the table, your hand, paper, and even other water molecules. This stickiness is what allows water to move through the coffee filter, taking all of the colors with it and mixing them together.

The Discovery Center’s Capillary Action Snowflakes activity encourages visitors to develop their observation skills and practice using science tools. This activity provides a fun introduction to the properties of water, by exploring the scientific concepts of capillary action, adhesion, cohesion, and surface tension.

During the activity, children create a model of a snowflake using coffee filters, scissors, markers, and water. Using this model, grownups are then able talk with children about the properties of real snowflakes, and how a real snowflake is, and is not, like the model they make.

Creating Capillary Action Snowflakes also lets children experience how primary colors mix together to form new colors.

Capillary Action at Home

You can continue your Capillary Action explorations at home by

Making Capillary Action Snowflakes at Home

Experimenting with Colors & Water

To create your snowflake:

Help each young scientist fold one whole coffee filter over itself to create a half-circle. Then fold this half-circle in thirds (see image at right).

Help children use the scissors to cut away pieces from the edge of the filter to create a snowflake pattern.

Help children carefully unfold the filters.

Have children use the primary-colored markers to gently color the coffee filter paper.

Help children lay the colored filter flat on a tray or plate and slowly add drops of water with a pipette.

Tip for Grownups: Less is more when it comes to adding water.

When children have finished adding water, help them lay the filter on a paper towel and blot it with a second paper towel. The snowflake is “finished” whenever they like - it’s ok to let some of the filter stay dry.

Questions to Think About While You Experiment:

  • What color is a snowflake?
  • Using only primary colored markers (red, yellow and blue), can you make a purple snowflake?
  • What does snow feel like?
  • What different shapes can a real snowflake be?
  • How many sides does your snowflake have?
  • Can you make two snowflakes that are exactly the same?
  • What is snow made out of?
  • Thinking About What Makes Water 'Sticky'

    Capillary action is the result of adhesion, cohesion and surface tension.

    Cohesion is the force that holds molecules of water to other molecules of water.

    Adhesion is the force that holds water molecules to other materials - like your hand, or paper fibers.

    The water molecules at the surface of the water are affected by surface tension - water molecules at the surface cohere to the ones just below more strongly because there are no water molecules above them to cohere to.

    In the Capillary Action Snowflakes activity, the water molecules at the surface of the water also adhere to the molecules of paper fiber in the coffee filter.

    The force of adhesion between water molecules and the paper fibers in the coffee filter causes the edge of the water droplet to be pulled into the air spaces* between the paper fibers. At the same time, surface tension holds the surface of the water intact, so instead of just the molecules at the edges of the droplet moving into the air spaces between the paper fibers, the whole liquid surface is dragged along into those air spaces. *The ‘air spaces’ are the small holes you can see in a coffee filter if you hold it up to the light.

    More to think About While you Experiment:

  • What happens when you drop water on the filter paper?
  • Look at your snowflake through a hand lens. What do you see?
  • Can you see the water moving through the filter paper?
  • Why is the water moving?