I have a PHD Minimus bag with 900 fill power down. It weighs 340g (12oz) and is rated to 8C. I have slept in it wearing merino socks, long johns, long sleeved top, and a balaclava with the bag in an Alpkit Hunka bivouac bag, on top of a Therm-a-rest Neoair when the temperature dropped below 0C...