Thermal labels are heat sensitive, so they'll slowly fade when exposed to direct sunlight or heat. But! Do not fear! Even after 3 months in the sun, they'll still scan. We use them for all our parcels, and we've found we can still scan them after 6 months. They'd have to sunbathe for an absurd amount of time to be unreadable. So the long and short of it is, if you're printing something like a barcode that won't be in direct sunlight, you can expect it to stay scannable for up to a year. Just maybe don't take the package to your sunny beach holiday in Majorca.