The bathtub is the perfect place for toddlers and older kids too to have fun with LEGO. How about exploring physical changes with a simple melt and pour soap activity! Your kiddos will love this soapy LEGO theme way to get clean! Perfect for kiddos who are mad about LEGO building! This homemade LEGO soap activity is easy to do and will take care of a few germs in the process.

Make Yourself LEGO Soap

Making homemade soap is a fun and easy activity for kids and it may just encourage them to actually use it at bath time!

This LEGO soap cleans away the dirt and grime then rewards the kids with a fun surprise as the soap wears away – LEGO mini-figures! You can make just a couple for home or make up a big batch to give as gifts.

Enjoy more fun in the bath with homemade LEGO bath bombs or glow in the dark bath paint!

What Is Physical Change?

Physical changes are changes that occur in matter without changing its chemical composition. In
other words, the atoms and molecules that make up the matter stay the same; no new substance is formed. But there is a change in the appearance or physical properties of the substance.

There are several physical changes, which are actually changes in states of matter that kids can see when making soap. First, you start with a solid glycerin soap base which needs to be melted to pour into the molds.

Then it becomes a solid again as it cools. Of course, if you put it in the refrigerator for a few hours that process happens even quicker! Whether you have liquid or solid glycerin, you still have the same substance.

Time to turn your finished LEGO soap into suds in the bath! Another physical change! Check our lots more examples of physical change!

Click here to get your FREE printable LEGO activities calendar!


Make washing up extra special with this special LEGO soap!


Alternatively, you could use LEGO soap molds like the ones we used for making our own LEGO crayons!


STEP 1. Cut the glycerin soap base into 1”x 1” squares with a sharp knife.

How many will I need?

  • How many you will need depends on the size and shape of your soap mold (you can even use silicone cupcake liners in the metal pan for stability).
  • To figure out how many you need the first time you use your mold, estimate based on the size of your soap mold.
  • Each rectangle in my mold fit roughly 4 of my one-inch squares. So to make two I used 8 one-inch pieces and two extra to compensate for where they didn’t quite fill in the mold.
  • If you have a little soap base leftover don’t worry you can pour it back in the package and let it reset-it will melt and pour over and over again.

STEP 2. Fill your soap cavities with the LEGO mini-figures. Be sure some of the mini-figs are facing down, touching the silicone mold so you can see them when your bars are done!

STEP 3. Place the squares in a large glass measuring cup with a lip. This makes it much easier to pour into the molds.

Then melt the glycerin base in the microwave in 30-second increments, stirring each time, until fully melted. Mine took 90 seconds.

STEP 4.  Quickly stir in your essential oils if using.

STEP 5. At this point, your soap mixture will be very warm but still safe to touch, Use a towel against the warm glass and carefully pour your soap mixture to fill each cavity to not quite full.

STEP 6. Have an adult carefully move the mold to the refrigerator so it will set faster. Leave your bars alone at least 2 hours, the waiting is hard but it will be worth it!

Once set carefully remove the soap from the mold. Your LEGO soap is now ready to use!

Wash and repeat until just the mini-figure is left!

More Fun With LEGO

Printable LEGO Brick Building Pack

Breathe new life into your existing LEGO or brick collections!

Grab the whole Brick Building Fun Pack in our SHOP

What’s Included:

Anytime this bundle is updated, you will be sent a new link. Update coming this summer.

  • 10O+ Brick theme learning activities in an e-book guide using the bricks you have on hand! Activities include literacy, math, science, art, STEM, and more!
  • Brick STEM activity challenges complete with instructions and examples such as a marble run, catapult, balloon car, and more.
  • Brick Building STEM Challenges and Task Cards keep kids busy! Includes animals, pirates, space, and monsters!
  • Landmark Challenge Cards: Virtual tours and facts to get kids building and exploring the world.
  • Habitat Challenge Cards: Take the challenge and build your own creative animals in their habitats
  • Brick theme I-Spy and Bingo games are perfect for game day!
  • Screen-free coding activities with a brick theme. Learn about algorithms and binary code!
  • Explore mini-fig emotions and much more.
  • A complete year of Brick themed seasonal and holiday challenges and task cards
  • Brick Building Early learning pack filled with letters, numbers, and shapes!