Originally Posted by
gauvins
We have 40F rated down bags and are planning a trip where the average expected minimum temperature is 37F. So we are planning on a freezing night or 2. We may be able to find some kind of accommodation if the temperature were to drop way below normal, but would rather be safe (read -- "warm") than sorry.
We sleep in a single walled tent.
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I have used a 40 degree bag when there was frost on the ground, but it was above freezing in my tent. Your tent will add several degrees, so I think you do not need to worry about 37 degrees.
I assume you have slept outside when it drops below freezing before. But if not, think about anything you have that contains water in it. Water bottles that you can't get the lids off later because they are full of ice, cans or bottles of wet food (soup, soda pop, etc.) can be damaged. A water filter that has some water in it can crack, I always bring my filter into the tent if it is going to be cold outside at night, a friend of mine had his filter crack in sub freezing weather. Cooking pots that have ice in them that has to be removed before you can make food or pack up. Etc. Even if the forecast is for above freezing, in localized low spots it can get quite chilly and below freezing.
Originally Posted by
gauvins
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We have silk liners. We have head gear, thermal undies and metal bottles that could be filled with warm water. We also have emergency blankets that can be used next-to-the-skin or as a sheet, over the bag.
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Yean bring your liners. I have not found liners to be effective at adding warmth, but others disagree with me so maybe they work and I just have not noticed it. I use a liner more to keep my sleeping bag clean than for warmth.
Head gear, I assume you mean something like a stocking cap. Absolutely. I usually sleep with a stocking cap when camping in cool or cold weather. One that does not have a tassel on top since the tassel gets in the way. A skull cap shape made from polartec or something warmer like wool would be great. An acrylic stocking cap that is more for looks is not very effective, if you have one leave it at home and get a better one.
Thermal undies, yeah wear them.
Metal bottles with warm water, skip it. They won't add much warmth for 7 or 8 or 9 hours. You do not need that much warmth for the first hour or two, you need warmth at 4 or 5 am and by then the water will have reached an equilibrium with the temp inside the bag.
Emergency blankets, I think you are best off to not put over the top, maybe put them under the sleeping pads on top of tent floor if you think that they can add some insulation value. (Years ago a friend of mine used to use a space blanket on top of his tent floor for winter camping for the insulation value.) I say do not put on top because you want moisture that gets into your bag to be able to escape through the shell of the bag. But, if you are really freezing and will have an opportunity to air out your bags later, then maybe the short term gain of warmth might help a bit?
Sometimes in cold weather I have draped a down jacket or down vest on top of my sleeping bag in the torso area. But never anything else because a down bag will easily compress so you do not want to put anything that is denser than down on top as that could compress your insulation.
Originally Posted by
gauvins
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(1) We have to purchase new sleeping pads, which brings this specific question: One is rated R 3.2, the other R 5.7. The penalty for more insulation is something like 150 grams (5 ounces) and $50. does it make a meaningful difference? (therm-a-rest claims that it does...)
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No opinion, I have no clue what any of my pad R ratings are. I have only worried about the insulation value of my pads when sleeping on top of packed snow.
Originally Posted by
gauvins
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(2) What about sleeping bags covers or bivies. Said to extend the range by an additional 5-10 degrees F. Hype or not?
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I would not bother with additional covers. Recall my comment on compressing your down insulation. You are already in a tent that will trap some heat in it.
I have a regular length winter bag but I should take a long one. My feet can compress the bottom of the bag because of the shorter length. I have found that down booties or down socks really help in that bag. If you occasionally get cold feet at night (some people do), consider warm socks at night. But if your feet start to sweat, then maybe the socks are not a great idea.