heat reactive fabric/material

[kobi]

which type of fabric can be made to change colour the hotter it gets . i remember these tshirts that changed colour. it started out light blue then if it got hotter it slowly turned pink and if you ironed them, it went dark purple straight away.

also, mcdonalds gave away a pair of blue kids glasses that turned purple when the sun got warmer.

does anyone know how they do that?
it was like magic

[heathfield]

It's not the fabric, but dyes that react to temperature change. For example, have a look at 'Leuco dyes' here