One of the old stories that circulates around the backpacking world is that you’ll sleep warmer if you sleep naked (as opposed to “nekkid,” in which case you’re still undressed, but also up to somethingB). I have no idea where that tale got started, but it still pops up occasionally, and probably has helped foster confusion over what to wear in a sleeping bag.
Yes, I skip the high heels, but I always wear something. This is for two reasons. The first is warmth. The more you wear inside the sleeping bag, the warmer you’ll be. Plus, by wearing most of your clothes (which you have to pack anyway), you can take a lighter sleeping bag, shaving a pound or two from your load. I’ve successfully used summer-weight bags pretty high on Mount Rainier with that technique. Just wearing a light long-underwear suit (with long sleeves), plus socks, light gloves, and a soft hat will add an amazing amount of warmth to your sleep setup and probably five to ten degrees to your bag rating. Put a fleece jacket on over that same setup and you’ll add another five degrees to the bag’s warmth. So, where you might have needed a 20-degree bag, you can now get by with one rated 30 to 35 degrees.
The other reason to wear clothing to bed is that it helps keep the bag cleaner. Your skin is a real greasepit after a few days outdoors聴sweat, bug repellent, ground-in dirt, spilled camp coffee, and gawd only knows what other bodily secretions. A light layer of long underwear聴at the very least a T-shirt聴helps keep crud off your bag. So you have to wash your bag less, it lasts longer, and your bank manager’s happy with your limited purchases of new gear.
So there you go. Dress right, sleep well.