Be careful with those. Their ink is erasable because of the heat generated by friction (hence the name), which also mean content can be erased by other heat sources or in some situation like a notebook put in a car parked under the sun in summer. Moreover, doesn't seems super durable, so for notes that much be keep for long time, it is also not the best solution.
The reverse is true though, try putting it in the freezer and you'll see ;). Erasing them doesn't actually remove the ink, it just make it transparent.
