Pilot Frixion series is the best erasable pen on the market. The Pilot Frixion series applies a special thermosensitive ink. You can easily erase your mistakes with the special Frixion rubber. The special pilot ink technique - when the temperature reaches the point, the ink becomes transparent simply by rubbing with the rubber at the end of the pen. The change of the ink is based on the change of temperature and won't leave any dirt. This Pilot Frixion ball knock gel pen is retractable and refillable. Please note because of the thermo-sensitive ink, it may be not suitable for important mail and documents.