Rubbing makes the ink transparent. Uses a unique "friction ink" that disappears when the temperature rises above a certain level. When you rub the handwriting with a special rubber, the color of the ink becomes colorless and transparent due to the frictional heat generated. No erasing residue appears even when rubbed. Since the ink is made colorless by using the temperature change, there is no erasing residue. Handwriting that has entered the eyes of the paper can be erased cleanly if the temperature is transmitted, so there is almost no unerased residue. You can write and erase anything. You can rewrite it over and over again in the place you erased once. * Friction is an erasable writing tool. Please do not use it for things that cannot be erased, such as certificates and addresses.