I've used it outside and inside on the hottest days that there were games...some of them were beyond, "we really shouldn't be running around all geared up in this heat" hot.
Indoors winter where it's cool-chilly...it still works, but not a nice.
Cold enough to see your breath...forget it.
So...15c - 35c?
Do not leave your mags filled with gas out in the sun during the summer! i.e. on the hood of the car, on the dash, etc...