What is the principle that the words written by erasable pen disappear after heating and reappear in the refrigerator?

The principle of erasable pen handwriting disappearing and appearing is thermal reaction. The ink of erasable pen contains special polymer materials, including color developing agent and color changing agent. At room temperature, the color developing agent and color changing agent combine with the color developing material on the paper to form an erasable pigment film, thus producing the color of handwriting.