The OEM Pilot Frixion Highlighter pack includes three erasable highlighters that allow you to highlight and erase repeatedly without damaging books or documents. Featuring a thermo-sensitive ink formula, the ink disappears with erasing friction. Please note that these highlighters are not recommended for use on official legal documents, as exposure to high temperatures can render the ink colorless. To restore the color, simply cool the highlighter to at least 14 degrees Fahrenheit in a freezer. This product has also earned the prestigious Good Housekeeping Seal.