2nd Class (Ms Hackett) Heat Changing Slime

We made heat sensitive colour changing slime. The slime is made using thermochromic pigment allowing it to change colour based on the temperature of the slime. Thermochromic pigments are available in a wide variety of colours and temperature ranges, so you can change the colour of the slime using cold or hot temperatures.


  • 5oz PVA glue
  • 1 tablespoon baking soda
  • 2 tea spoons saline contact lens solution (needs to contain borac acid)
  • 1/2 teaspoon thermochromic pigment


  • Mixing bowl
  • Measuring spoons
  • Small airtight container for storage


1. Combine the PVA glue and baking soda. Stir together until mixed. No lumps or clumps!

2. Add the thermochromic pigment.

3. Add in the saline contact lens solution. Add one teaspoon at a time. The slime mix will begin to clump together around the spoon and pull away from the sides of the bowl.

4. Knead the slime – remove the slime from the bowl (don’t worry if it is super sticky!). Knead the slime between your hands for a couple of minutes until the stickiness fades and it becomes more solid.

5. Time for colour changing! Once your slime is done you can change your colours in a variety of ways – for example, we used a hot-water bottle to heat it up and an ice-pack to cool it down.


  • Temperature effects the colour of the slime.
  • When the slime is heated it changes colour (caused by the thermochromic pigment).
  • When the slime is cooled down it returns to its original colour.

Fun Facts:

Thermochromic pigment is what causes heat sensitive rubber ducks to change colour! This lets parents know if the bath water is too hot!

It is also used in mood rings and thermometers!

Post Author: Ruth Hackett