murwilson wrote:Don't wear all your clothes in a sleeping bag, you'll get cold. A sleeping bag is designed that it needs the heat from your body to get into it for it to work. If you wear lots clothing in the bag it will trap some of the heat, the bag won't get up to its optimum operating temperature and you'll feel cold. If you want\need to wear clothes, loose fitting, like your jammies should do the trick nicely.
If you're still cold, place your down jacket or other shell on top of the sleeping bag, like a quilt.
Mur
I just don't buy this approach. I've heard others say it before and it's no more convincing for me the more times I hear it - it doesn't make sense, and it goes totally contrary to my personal experience. Before I waffle on (at length) here's a TL;DR version:
An extra barrier of insulating material between the warm air and the cold air keeps the warm air in and the cold air out.
The way Mur's argument goes (and he's not the first to voice it, I've heard others suggest it as well) is that you want the air inside the sleeping bag to be warm, so you get this warm bubble surrounding your whole body. And without outside interference, the quickest way to get this air warm is to stop it being trapped close to your skin (by your clothing.) So sleep pretty much naked to warm the bag.
Now if you're wearing a down jacket the heat from your upper body will largely will be trapped. So it'll take longer before the air inside the sleeping bag gets warm. Over time - and at a slower rate than without the jacket - the air in your bag will start to warm (provided the bag has minimal circulation, good baffles stopping the air escaping etc.) But it'll take longer than if you weren't wearing the jacket to warm the bag.
But that doesn't matter. Because the air close to your upper body is still warm. It's being trapped by your clothing. Yes, the areas that aren't clothed will feel colder, but ultimately more hot air is being trapped right against your skin. Well fitted clothing will mean less air to heat - there's a lot less air between your skin and your clothing than is contained in a sleeping bag, so it takes less heat.
And even the best bags aren't airtight. You move in your sleep, you force hot air out of the sleeping bag. Hard warmed air. With clothing you've got an extra layer to stop that heat loss.
Put it another way: it's like saying not to use a second sleeping bag as an inner because the hot air won't get into the outer bag. It just doesn't add up - an extra layer, an extra barrier is always going to trap more heat. Yes, if you disrobe to warm the bag the heat will be shared more evenly around your body but there will be less heat inside the bag - full stop.
The 'jacket as quilt' thing just doesn't make any sense - if draping something loosely over you was the most efficient way of trapping heat we'd all be wearing down ponchos instead of down jackets. And if you move much it'd slip off at the first scratched elbow losing any heat it was trapping (not that it'd be much anyway.)
I'd share stories of my own experiences to support my story but I'm sure those who disagree will have their own. Perception can't always be relied on (mine or anyone elses.) So I'm happy to stick with the beer mat science instead.
Oh, I agree about the sleeping mat though - down when compressed (under you) offers virtually no insulation. Your sleeping mat is the only insulating barrier between you and the cold ground.
(And Mur, whilst I've at length disagreed with almost everything you've said - it's nothing personal, and I'm just sharing my view for the same reason we all do on here - to try and help out others. So I hope there's no hard feelings
)