Marshmallow madness

So this one is fun but obviously not one to do if you don’t want your child consuming large quantities of marshmallows. What you need:

  • Microwave (essential)
  • Oven (essential)
  • Packet of marshmallows (essential)
  • Giant chocolate buttons and mini marshmallows (not essential but make a nice hat for the snowman!)
  • Nutella (not essential but again good for decoration)
  • Cocktail sticks (not essential but do stop your snowmen collapsing in the oven!)


What to do:

  • Make some mini snowmen. We didn’t use a cocktail stick to pin them together but I would do this if I did it again as ours all collapsed. Kid M named ours evil snowman, sad snowman and happy snowman so you can tell I was pretty good with the decorating as that was obviously what I was going for!
  • Heat oven to 50 degree c and pop snowmen in on baking tray. Heat up for 5 minutes.
  • Remove from oven (obviously be careful, don’t let the kids do this, etc) and see what has happened to the snowmen. Give them a squeeze. Consume 🙂


  • Put single marshmallow (with face if feeling creative) on a plate in the microwave for 10-20 seconds on high (ours is 800 watts).
  • Watch the marshmallow through the door. Be amazed!
  •  Consume (if desired – be careful as it can be very hot).

The science bit

So this might all seem a bit strange but the marshmallow doesn’t necessarily behave how you think it will. When it gets heated up in the oven the marshmallow begins to melt. Marshmallows are mostly made up of sugar and water. As the marshmallow become warm the sugar softens and so makes the marshmallow squishier.

When the marshmallow is in the microwave something slightly different in happening. A microwave works by heating up the water. So the water in the marshmallow gets hot and heats the sugar, again softening it. However, there are also air bubbles in marshmallows that get heated up by the hot water too. Everything happens quickly and at the same time. The air molecules in the bubbles move about faster when they are heated up and push against the bubble walls, making the bubbles get bigger. As the sugar is softened the expanding air bubbles cause the marshmallow to puff up. If the bubbles expand too much they will burst and the marshmallow collapses.


Tips/extra bits:

  • Our marshmallow shrank almost the moment we opened the door of the microwave so definitely watch while it is heating up.
  • Give kids a spoon (or chopstick in our case) to play about with the melted marshmallow as it begins to go stiffer once it cools. This is because the sugar hardens again and some of the water has evaporated off.

Explaining it to children

It was quite good that our oven marshmallows just went a bit squishy rather than full blown melting as Kid M could test the difference by feeling the pre-oven and post-oven marshmallows (warning: this can lead to your child ending up slightly sticky and probably consuming the snowmen). We did this bit first and I then got her to think about what would happen when we put a marshmallow in the microwave.

She guessed it would melt as microwaves make things hot but was amazed to see it grow in size. I explained the bubbles inside the marshmallow were expanding like a balloon and because the marshmallow was warm and squishy, and therefore could move about more like the ones that had been in the oven, they grew in size with the bubble. The balloon analogy works with the bubbles expanding too much and bursting as well.


Experiment based on an activity from the fantastic Exploratorium: The science explorer book.

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