In the beginning of the 90’s there was an amazing movement, that astounded even the most creative minds. No, it wasn’t Peter Andre’s surprising success or the slow demise of the perm, it was the hypercolour T-shirt.

For those unfamiliar with this fashion craze, the concept is easy: people were purchasing fabulous clothing that changed colour when they heated up or cooled down. And let me tell you, as soon as you put on one of these shirts, you’d be cooling down in an instant. As people danced through the night, they’re bodies would heat up and their clothing would give it all away. So how do these T-shirts work? How can a material magically change colour due to heat? Well! There ain’t no magic involved, other than the magic of science!

Thermo-chroming

Substances that can change colour due to a change in temperature are called thermochromes. There are two types of thermochromes: liquid crystals (used in Mood rings) and leuco dyes (used in hypercolour T-shirts). Liquid crystals are made of carbon molecules which are attached to each other in a way that is very sensitive to changes in temperature. This means that when the temperature changes, how the carbon molecules are attached to each other, also changes. When the shape of the molecules change it makes the crystals absorb light and reflect wavelength differently. Because our eyes see colour as wavelengths, when the crystals reflect wavelengths differently it looks as if the colour of the shirt is changing

Leuco dyes, the power source of the garment in question, are very similar. Leuco dyes are put into tiny capsules, along with other chemicals, and this capsule is then applied to the T-shirts. When it is cold the mix in the capsule is solid and the carbon molecules in the leuco dye are attached to each other in a ring shape. When we heat up, just like liquid crystals, the molecules change shape. They break open the carbon ring. This change means that the dyes absorb and release light differently, and the colour we see is different. Leuco dyes are also used in colour indicators on batteries, to show us how much life the battery has left in it.

So, next time you start excessively sweating on the dance floor, try blaming the colour change in your clothes on thermochromatics. It won’t be true (unless you happen to be wearing a hypercolour shirt), but while they pause to think about what you just said, you might have some time to escape an awkward situation.