Thermochromic (TC) products predominantly change color in response to temperature fluctuations. There are two primary types of TC’s, liquid crystals and leuco dyes. The most famous TC application ever, the "mood" ring of the 1970’s, was a liquid crystal. Today, liquid crystals are used in many products, including forehead thermometers, room thermometers; game pieces stress testers, and other applications. While liquid crystal TC’s are extremely capable materials, they are difficult to work with and require highly specialized manufacturing techniques. The other type of TC is called a leuco dye and is commonly used in advertising, consumer packaging, product labels security printing, novelty applications such as temperature sensitive plastics and mugs, promotional items ,toys and textiles. Thermochromic permanent change ink is a high temperature activated, permanent change pigment.
Leuco dyes are less precise, easier to work with and commonly used for packaging, product labeling/graphics, toys and novelty applications