FriXion Light Erasable Highlighters allow you to highlight and erase repeatedly without damaging books or documents. Thermo-Sensitive Ink Formula disappears with erasing friction. Erasable highlighters are not recommended for use on official legal documents. If the highlighter is exposed to a temperature that reaches 140 degrees Fahrenheit, the ink will be colorless when highlighting. To restore color, cool to at least 14 degrees Fahrenheit in freezer, and the ink will highlight in color again. Highlighter also earned the prestigious Good Housekeeping Seal.