As I see it there are two parts to keeping warm, that is when you're awake and when you're asleep.
People have said moisture is a key consideration and for me it's really the main one because I sweat a lot, even in my sleep, and even when I'm not particularly warm.
When I'm walking or working I don't like to use plastic coated waterproofs for any length of time because they just soak me through with condensation. I need to let the moisture evaporate, so for me plently of layers of fairly loose weave fabric, not fitting too tightly, seems to be best.
Like Man of Tanith when sleeping I like to put some heat near my feet, that's where most of the moisture ends up because that's where the bag is coldest. The heat drives the moisture away very easily. For me it's usually a hot water bottle but I also occasionally use a Zippo hand warmer. The Zippos create a little moisture by burning the fuel. It isn't a lot, something like 20ml on a 12 hour fill, and to be fair that's much less than I would lose in sweat in the same time, but it's worth knowing. One advantage of the Zippos over a hot water bottle is that they can't leak! If I do use a hot water bottle I generally put it inside an Ortlieb dry bag as a backup in case it leaks.
One hot water bottle in a decent sleeping bag should be more than enough heat to keep anyone warm enough in almost any British winter. For me it would be far too much if the water bottle had no insulation, so I wrap it in lots of clothing, towels or whatever. That drives moisture out of the insulation so you have drier clothes in the morning and it reduces the rate of heat loss from the bottle so it makes for a gentler heat which lasts a lot longer. In the morning if I can't hang things out to air, perhaps because the weather is too wet, I refill the hot water bottle, put it on my folded sleep mat and heap all my sleeping gear on top. That drives most of the night's moisture out ready for the next night.
I use a breathable bivvy bag over my sleeping bag. Often if I'm in a tent it won't be quite long enough and the foot of the bag touches the tent wall, which is usually damp with condensation. The bivvy bag stops the condensation wicking into my sleeping bag, and when moisture is driven outwards by body heat it doesn't all condense on the sleeping bag outer shell, it keeps on going to the outside of the bivvy bag.
Heat-reflecting layers and linings are really excellent. They give tremendous extra heat insulation for practically no extra weight. Be aware that they don't generally breathe moisture at all.
I agree with the sentiment that it's a lot better to keep warm by insulating your body than by trying to heat the space you're living in. Heating a tent is a very inefficient way of using heat, I dread to think what the 'U' value of a typical tent would be. :yikes:
People have said moisture is a key consideration and for me it's really the main one because I sweat a lot, even in my sleep, and even when I'm not particularly warm.
When I'm walking or working I don't like to use plastic coated waterproofs for any length of time because they just soak me through with condensation. I need to let the moisture evaporate, so for me plently of layers of fairly loose weave fabric, not fitting too tightly, seems to be best.
Like Man of Tanith when sleeping I like to put some heat near my feet, that's where most of the moisture ends up because that's where the bag is coldest. The heat drives the moisture away very easily. For me it's usually a hot water bottle but I also occasionally use a Zippo hand warmer. The Zippos create a little moisture by burning the fuel. It isn't a lot, something like 20ml on a 12 hour fill, and to be fair that's much less than I would lose in sweat in the same time, but it's worth knowing. One advantage of the Zippos over a hot water bottle is that they can't leak! If I do use a hot water bottle I generally put it inside an Ortlieb dry bag as a backup in case it leaks.
One hot water bottle in a decent sleeping bag should be more than enough heat to keep anyone warm enough in almost any British winter. For me it would be far too much if the water bottle had no insulation, so I wrap it in lots of clothing, towels or whatever. That drives moisture out of the insulation so you have drier clothes in the morning and it reduces the rate of heat loss from the bottle so it makes for a gentler heat which lasts a lot longer. In the morning if I can't hang things out to air, perhaps because the weather is too wet, I refill the hot water bottle, put it on my folded sleep mat and heap all my sleeping gear on top. That drives most of the night's moisture out ready for the next night.
I use a breathable bivvy bag over my sleeping bag. Often if I'm in a tent it won't be quite long enough and the foot of the bag touches the tent wall, which is usually damp with condensation. The bivvy bag stops the condensation wicking into my sleeping bag, and when moisture is driven outwards by body heat it doesn't all condense on the sleeping bag outer shell, it keeps on going to the outside of the bivvy bag.
Heat-reflecting layers and linings are really excellent. They give tremendous extra heat insulation for practically no extra weight. Be aware that they don't generally breathe moisture at all.
I agree with the sentiment that it's a lot better to keep warm by insulating your body than by trying to heat the space you're living in. Heating a tent is a very inefficient way of using heat, I dread to think what the 'U' value of a typical tent would be. :yikes:
