.... sorry about being such a pest about this , everyone was fantastic with my other post "down vs. synthetic" ... but it's getting down (pun intended) to it now .
So for certain "Down" is my choice , and I had said 0* was my target temp. , but the more I research and read about down bags the more questions I come up with .
A big one is this , "Why not a lower temp. rating instead" (sub-zero ratings) ?? ... it's doubtfull I would ever be in camp at 0* let alone -20* or -40* (F.) , but nights that snap to 10* have surprised me before .
If I was to use the -20* or -40* bag , "would I be simply miserable" and toooo hot in +20* to +40* night temps. , which would be most common for me .
Just how versitile of a temp. range should one expect with a down bag ... I know you can unzip and vent , and some are able to be use like a blanket .
I have also pretty much decided to shop used , probably eBay , there are sooo many nice hardly used used bags there at considerably less $$ than new ... reputable brand names too like Marmot , North Face , MontBell , etc. (most are real , not fake counterfiets) .
Another thing is , practically all the single down bags don't unzip all the way to the feet , and probably won't be joinable together to make a double (Adam and Eve) bag , so we may be stuck with independant sleeping (don't really like that idea when we are together) ... but I would need an independant bag 60% of the time anyway (she won't be there) ... two compatable joining bags that can be independant or double when joined doesn't seem like it's going to happen ... took a shot at two North Face (a matching pair of left /right zips , -5 degree) , but lost that one (I was second highest bidder at around 420. for the pair) ... doubt I'll see anything like that again ... probably would end up with two different manuf. and style bags from eBay .
Sometimes I think that I should just get a high end sub-zero bag (single) for me only , when I'm out in the mountains with nephew and the guys only ... and then get a less expensive double bag for temps. when she would be there , like +40* or more ... Cabella's seems to have a nice double bag (down on top , synthethic bottom) ... but the next thing ya know , she will want to be going out with me everytime ... I find it difficult to prepare for her new love of "my" thing !!
mating bags
Mummy bags don’t usually unzip all the way to open flat, but that doesn’t mean they can’t be mated. You just need to have a left-zip bag and a right-zip bag. They just mate along the zipper, and retain two separate foot-wells No playing footsie this way, but all the other . . . well, you get the picture. 
I’ve always been comfortable in my 20 degree bag down to about 30, which is about as low as I tend to go camping. When it’s up in the 50s, I sweat, any sleep with the bag open. I don’t see any good reason to buy a colder bag than you need though. Some sweating is unavoidable when you’re way outside the temp rating, so if you don’t plan to camp below 20 degrees, I definintely wouldn’t buy a bag lower than 0 degrees.
If you anticipate
a colder night, wear something warmer (fleece) when retiring so you will sleep warmer. Getting a bag rated for to cold is about as bad (or worse) than one for not cold enough.
temp ratings
I’m a cold sleeper - means I’m usually cold. a 15 or 20 degree bag works fine for me all year - when its really warm and humid out, I end up half out of the bag anyway. a lightweight fleece pant and top, a warm hat, some warm socks, and a hot water bottle near the feet, and that 15 degree bag will keep me warm enough to sleep a few hours at 5 degrees out.
The story I heard about bag ratings was the SAS conducted their rating tests where the soldier would sleep out on a 3/4" pad, no long johns, no shelter…if he could sleep for a couple hours at that temperature, that was the rating the bag got. Minimum survivable rating.
No such thing…
as a perfect bag for all seasons.
If you buy a -40 or -20 and you try to use in +40 temps you’ll be miserably hot and won’t get any rest. If you buy a +40 bag and try to use in 10 you’ll freeze and won’t sleep.
While not practical $$ wise it is necessary to have bags for cold, cooler, and warm weather if you’ll be sleeping out of doors in all these ranges.
I own no less then 5 different bags. The “coldest” is my North Face +20 synthetic mummy, then I have a Mountain Hardwear Flip semi rectangle (once side is supposed to +25, the other +0) which is really only good down to about +35, I have an ultralight Slumberjack +40 rectangle, a good ol’ Coleman rectangle for cabin use, and simple fleece rectangle for really warm nights in the tent.
I’ve encountered a few nights that my NF mummy isn’t quite warm enough for, so I’m planning to add a +0 mummy to the inventory - probably down.
I’m sure some people make due with a smaller bag selection, but I haven’t figured how to be that person. But I also by mid range bags, not top of the line because I don’t use them often enough to justify the expense.
From your other post and this one it sounds like you might need a good quality +0 mummy bag, and good quality +25 or +30 bag for your trips without your wife. For the trips with her some sort of larger Jack & Jill bag to be shared, or perhaps to individual rectangles that could be zipped together.
X-fibre
I bought a couple of mummy bags made by Backside that are filled with a synthetic down and rated for 15 deg. They can be zipped together if you want. Used them in 40+ deg temps and they were too warm.
As advised already, for more warmth with a lighter rated bag just wear some long underwear, hat, socks, in your bag. Really makes a difference and not as bulky as a heavier bag.
Tom
Adapt & overcome
I use a Kelty 40F rated bag that packs to the size of a football. For cooler weather, we bought 4 yards of polartec fleece from a fabric store ($20) and sewed it to make a a bag liner. I’ve been cozy in 30F nights using the combination and have the option to use the liner or not.
pads
Don’t forget that pads are a critical part of a sleep system. one of those ridgerest closed-cell foam pads will insulate better at the below-freezing temps, and can help with retaining warmth. Big Agnes has a 0 degree rated air-core insulated pad - foam on the bottom of the chambers, Primaloft filled, and if its warmer out, flip it over, and the insulation factor changes for the +32f nights. I’m sure there are other options out there - I;ve found that its way cheaper to get a couple of different pads and a “general use” sleeping bag, rather than the one pad, 2-3 bags solution.
yeah , I guess I really do know …
… that there just isn’t going to be “one” bag that will be “perfect” for every temp. condition I/we would be out there in … I was leaning towards the cold side of things probably thinking how to be best prepared for the worse case scenario for her (the just in case thing)
personally , I’m used to compromising every which way , cause I’ve always been a minimalist when it’s just me to consider …
but “now” trying to bring her into the bigger more “time out there” picture , I find myself always trying to bring the kitchen sink when she’s along , so she won’t have to go without anything … it’s the protecter provider thing ya know ?? … but it sure makes things more complicated !! … she loves this stuff so much I just want to bring her the luxurys that I never really was inspired enough to do for just me … I am a confused man , losing my grip because of a woman I want the “best” for … lazyness isn’t much of an option these past couple years with her onboard !!
When it get’s reasonably warmer 50’s on up , there are just so many options for camp sleep , including a simple blanket for cool summer nights … the only dbl. bag I have , and we use now has a built in air mattress and works OK at 40* , the air mattress can be taken out if desired , but it makes the ground softer .
Something else is that when together in a twin bag , each others body heat really adds up .
ps., … OMG , I just re-read my post and it sounds more like a “dear Abby” letter asking for life advise … I’m not sure how to deal with that ??
You can push the comfort level
of a twenty degree bag a little lower by adding a silk or Thermolite liner.
Thermolite claims fifteen degrees. Seven to ten is more realistic.
I use a forty degree bag down to thirty five with the liner.
Then switch to another entirely different bag for colder.
Some use a down bag for the temp they will usually use it at and then throw a fleece blanket or big higher temp rated sleeping bag over for colder temps.
Anyway you get the idea…buy what you will use the most…
I got the forty degree bag because with the “colder” bag I was usually miserably hot.
I wonder
How much more warmth you could add to a bag by putting a cover over it like a pillowcase? Seems the object is to trap heat within.
Tom
not sure you can quantify that
but on some of our trail maintenance trips on the Appalachian Trail near Mt. Katahdin it gets cold. I bring along the 20 degree bag. But its borderline in October when the temp gets to 20. That old down bag of temp rating unknown over the top does help.
The object is to trap air…and I think of it as somewhat like layering. The more dead air I have between me and cold is reassuring.
Surprise temperatures
I’ve had them on the low end and the high end of the temperature range.
For the high end, use the bag as a blanket. That’s about all you can do, besides opening all the tent flaps to maximize air flow.
For the low end, there are more options:
- Keep a couple of liner bags. A very thin one and a thicker fleece one. They and the sleeping bag can be packed separately, so they’re easier to pack in a kayak than one sleeping bag intended to cover the coldest possible conditions. Get a liner bag that can be unzipped fully, or simply use a light fleece blanket folded in half (I have both, and I’ve even used both inside a semirectangular sleeping bag, for the coldest car camping at 8 or 9 degrees F).
- Wear loose socks and a balaclava or HeadSokz to bed (in addition to long johns). These add a lot of warmth for very little additional bulk or cost. If necessary, wear another pair of socks on your hands as if they’re mittens.
- If you’re not already doing so, put your dry bags along the edges of the tent floor inside, forming a sort of heat shield.
- If you and your wife’s bags can be mated and you don’t mind being smashed together, that should increase warmth (I don’t know, because I hate being smushed together like that).
One Bag?
Why not just get one bag rated colder than you need just in case? Because the colder rated bag is bulkier,heavier,and usually more expensive.
Great Deal
Here’s a great deal on a 5 degree Mountain Hardware down bag: http://www.rei.com/outlet/product/789511 . Have no experience with this bag, but this is a very good company. This bag also has a full length zipper. I’m thinking about getting one myself. As suggested, get a thermolite liner for colder nights.
down sleeping bag
Check out your local venders and if not successful there, haunt the mark down section, sale, discount, bargain basement or whatever each vender calls the sale section of their website. Check out many.
I was just able to get a zero rated Marmot sleeping bag (800 fill down) at nearly 50% off from Hilton Tent City in Boston. Spent some time looking for a high quality down bag, long size, with a bit more shoulder room and then bingo it jumped out at me. Hilton had only one of that bag (now gone), but they have others and in this economy there should be other venders unloading the cold weather bags they ordered before the economic shit hit the fan. If you still have a job this should be the time to get a high quality cold weather bag cheap.
Dave
Some thoughts
If you want the possibly the best down sleeping system, try: Nunatak http://www.nunatakusa.com/index.html They make very high quality and creative sleep system. They make 2-person systems.
Another really great option is Feathered Friends. Their regular bags are the bees knees and their Rock/Winter Wren bags are really awesome. I know they look a little gimicky, but, they are super convenient. If it were a gimmick, they wouldn’t have been making and selling them for 15+ years.
Western Mountaineering also makes primo sleeping bags.
Unfortunately, it’s nearly impossible to get any of these at anything but MSRP. As you have noted, other higher volume brands (Marmot, Mountain Hardwear, etc. can be had at steep discounts if you look long and hard enough.
Down has a huge comfort range
more so than a synthetic so using a bag that’s rated colder than you need won’t result in misery. The compactability gives you a wider margin.
Safe paddling.
second that…
i have three, overbag, ultralight, and ultimate thule for really cold nights. i have found them to be vastly underrated - im comfortable on the average to about 10 -15 degrees below the rating, with the exception of the ultimate thule - it doesn’t get cold enough around here to test that…