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Having slept everywhere from snow to caves I'm afraid there's simply no such thing as a <1 kg sleeping bag that gives you *comfort* below zero. It's simple physics of thermal insulation.
You can possibly *survive* the night shuddering in full clothes if you wrap yourself entirely in any such bag and temperature doesn't go below 5ºC.
For proper sleep in anything sub-zero you need a 3 kg mummy sleeping bag, inflatable mat and tent.