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What is Welding with Chocolate?

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Welding with chocolate is an innovative and fun way of demonstrating welding and engineering principles in the classroom or at home. It was developed by TWI employee Philippa Moore back in 2007 and has been captivating children across the UK ever since!

The main aim of the experiment is to enthuse children and young people about Science, Technology, Engineering and Mathematics (STEM subjects), with a particular emphasis on welding and structural integrity.

Bridges are made of all kinds of materials in the real world, including wood, stone, metal, bamboo, and concrete. In this experiment we use a slightly different material, chocolate!

A simple bridge structure can be made using one bar of chocolate that spans the distance to be crossed.

Welding with chocolate 1

A box girder bridge, however, is made from a long beam in a box shape instead of simply a plank. In this case it is made by welding four chocolate bars together. This box shape makes the beam much stiffer. We weld our bars together by first heating and melting the edges using hot water in a suitable container, before joining them together in the required shape and allowing them to cool and solidify.

Welding with chocolate 2

We can then test our different bridges to destruction by putting weights on the top of the bridge at the centre of the span until it fails. This allows the following questions to be discussed and answered:

  • How much more load can you add to a box girder bridge compared to a plank bridge?
  • If/when the different bridges break, how do they break?
  • Why is a chocolate box girder bridge much stronger?
Welding with chocolate 3
Welding with chocolate 4

To download our factsheets please visit our resources webpage by clicking here, and try the experiment at home or at school.

To view a YouTube video of Welding with Chocolate click here.

To find out more please contact The Welding Institute's Younger Members' Committee by emailing:

For more information please email: