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the duvet is just as warm for half the weight/size
But you've got to add the sleeping pad to that.
I might get some foam and cut it to size but not sure about sleeping pad at all really. Depends if I'm cold and trying to sneak into buildings with cold/hard floors or warm and trying to find flat/soft grassy spots?
My current bag unzips all around so you can use it as a duvet but because it's a bag it's quite large in that form.
Utter exhaustion is the plan :)
hippy-
But you've got to add the sleeping pad to that... not sure about sleeping pad at all really.
Mmm, you're a brave one! You'll lose heat to the ground faster than you lose heat to the air (because air's a good insulator - soil is not). A sleeping bag doesn't provide much insulation against the ground because the down underneath you is compressed by your bodyweight.
I learnt this firsthand on my first few proper hiking trips in my teens - waking up fucking freezing in summer despite being in an old 1200g 3-season down bag - and scurrying to pile up all my spare stuff underneath me.
So unless you're very confident in your ability to find a nice wooden floor rather than a concrete block, or a bit soft pile of pine duff, I'd strongly recommend a pad. Personally I know that I am much warmer with a 450g duvet and a 400g pad than I am with a big 3-season bag on its own.
Blow-up pads are smallest and lightest, self-inflating and foam rolls are pretty big and bulky, foam rolls are usually warmest for their weight but not very comfortable. But here's a trick if you don't need the comfort of an inflatable - 3mm closed-cell foam from a rubber/plastics supplier is significantly less bulky than a standard foam roll, and it's still pretty warm - I have a square of it for a sit pad when hunting.
But really you need to test, test, test, rather than asking questions! Buy stuff secondhand, you can usually recoup your costs if it doesn't work out. I am actually moving back to the UK in a couple of weeks if you want to borrow my Alpkit duvet and an inflatable pad for a few nights.
For what it's worth in the cold house competition, my old uninsulated wooden house was so cold we had ice on the inside of the windows... it was a fucking grim place to live I tell you.
lae
The theory goes that insulation beneath you gets compressed, so it doesn't actually do any insulating anyway - that's what your sleeping pad does. So the duvet is just as warm for half the weight/size.
For example I find I am (almost) as warm in my 450g Alpkit duvet as I am in my 1000g StS summer bag. Also because it doesn't have any zips/toggles/hood, it has proportionally more insulation for its weight (if that makes sense). Plus I find I sleep better because I'm not constricted, that's a personal thing though.
The only downside is when one leg creeps out in the night and you wake up with one freezing leg. But personally I find that better than being woken from getting tangled up, which I do in a regular bag.
Polyprops are warmer than merino for the same size/weight, plus they dry much faster. On the downside they're stinky, so I only wear them at night. I've heard good things about capilene thermals but they're pretty uncommon here in NZ.
Relying on tiredness for a good night's sleep is a surefire path to utter exhaustion...