[egypturnash]

because of its heat-reacting properties, the ink may disappear if left out in a hot car or by a heater (the official temperature at which it “erases” is 60°C/140°F)

Oh man. "I used these pens a lot and now several years of notebooks are empty because there was a heat wave" is a tragedy waiting to happen.

[gffrd]

I had a friend who lost some notes to this: left a notepad in the car during summer, found later that some of the writing had "disappeared."

Paper is pretty insulating (thinking about paper within a notebook here), so I suspect most people will be safe, assuming they don't leave loose sheets of paper in direct summer sunlight on their car's seat for long periods of time…

Though, when I learned about their incident, I immediately stopped using a FriXion for any writing I might want to come back to in 2+ weeks' time.

[jldugger]

Well, I use them with a rocketbook. The intended use case is to record the note digitally when the notebook is full, and then intentionally heat wipe and reuse. Realistically, most of my notes are low value after weeks let alone years, but peace of mind is cheap!

[aftbit]

Does the ink reappear if left in the freezer?

[jldugger]

Yes. Or tip a can of compressed air upside down and the cold air that comes out can unerase