Pete Elliott in Glen Affric, 1°C
"First night just used Minimus bag and was cold. Second night I put the Filler bag inside the Minimus and was toasty. Different experience."
Technical Note: The Minimus bag is good for 5°C, but the temperature in the bothy dipped below that, so Pete simply put his Filler bag inside, a warm and lightweight solution to a common situation in British hills. With both bags he was well covered: the two bags together would have kept him warm down to -5°C.
You want to go as light as you can, but the temperature in the early hours can catch you out: a Filler bag makes good insurance.