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I'm preparing to go on my first ever backpacking trip and do not have a suitable sleeping bag. What are the factors I should consider when choosing one?

Personally I'm looking for the best value I can find and don't plan to do any extreme trips with this gear. The trip I'm going on will be three nights and I would expect most trips I take in the future will only be one or two nights. The overnight lows are only supposed to be around 45 degrees F where I'm going, but I'd like to be able to use this bag down to about 35 degrees.

Based on my research so far it seems the biggest factors are:

  • warmth,
  • compressed volume,
  • weight, and
  • price.

I've seen people mention that if you want to be comfortable in 35 degree weather you should get a bag rated for 20. As far as size and weight go, I have no idea what is considered good and where the law of diminishing returns really kicks in.

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1  
can you rent one before you make any purchases? Some stores (REI) offer them for rent sometimes. –  DavidR Jan 2 '13 at 20:11
    
@DavidR, That is an option I've considered, but for a sleeping bag it seems like most of the variables are pretty quantifiable so I'd rather take the $20-$30 dollars I would have spent on a rental and put it back into the bag I buy. It seems like moving from a $120 bag to a $150 one is not completely insignificant. –  Mike Deck Jan 3 '13 at 17:28

4 Answers 4

up vote 4 down vote accepted
  • Warmth -- This is after all why you are buying the bag. Not all bags rated for the same temperature will provide the same warmth.
  • Fit -- A bag that fits you closely, but not tightly, will provide better insulation and is more comfortable in my view. For this reason I prefer mummy bags. Rectangle bags will provide more movement room, but will generally be heavier and colder.
  • Weight -- Depending on how far you are hiking, the weight may matter anywhere from a lot, to hardly at all.
  • Fill Material -- Down or Synthetic. Down will generally compress more and offer more warmth for the weight, while synthetic will cost less and handle damp better. Look out when buying down bags, as I have noticed a lot of bags lately using duck down instead of goose down. Duck down is not as warm as goose down.
  • Performence when wet -- While down compresses better, it is not known for it's warmth when soaking wet. In high humidity situations, or in any case where you are concerned about your bag getting soaked, you may prefer synthetic fill.
  • Compression -- This is a function of your other gear. I have a very small pack which will not fit any bag that does not pack down to a pretty small size.

I don't list cost because I approach it from the "determine what I need, then find one that fits my budget" approach. That often means buying sales or second hand. The price tag on my bag is not a factor in the woods.

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You've hit most of the important factors. Also, you might see if you can borrow one for your first trip to see what you like/don't like about the bag.

When you buy, you need to decide what kind of fill you want - synthetic or goose down. They have different characteristics, and you'll want to decide what's important to you.

People have different ideas about what constitutes an acceptable weight. I use a goose-down Jacks-Or-Better quilt that weighs about a pound or so, but it wouldn't be unusual for someone to carry a bag that's a couple pounds or more.

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I think you've covered all the factors except shape. The shape is either rectangular or tapered at the feet (aka mummy). Tapering means less weight and less space to heat with your body, but also a bit less freedom of movement. Rectangular sleeping bags can often be connected together, which is good if you're a couple and want to share body heat (amongst other things). A recent trend started by Nemo is offering sleeping bags with a bit of extra room in the knees so that you can shift easier while sleeping and change your underwear without having to get out of bed (more important than you think!).

If you're looking for a sleeping bag for shoulder/winter seasons then also make sure that it has a hood/flap that goes around your head. This will allow more heat to be retained within the sleeping bag and keep your neck/head from being exposed.

Many technical sleeping bags offer a tiny pocket near the top of the zipper which allows you to store a watch/phone/etc. for easy access.

Finally, remember that you can add layering to a sleeping bag via liners on the inside (fleece, synthetic, silk or wool) or via a bivy/goretex sack on the outside (less common).

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Also, the top and bottom of a sleeping bags are not created equally, some are sewn differently or have a different mix materials on the bottom side to accommodate the fact that you're lying on it the whole time, but I think it's used mostly as a marketing tool and only has a minor impact in the overall quality of a bag. –  furtive Jan 2 '13 at 23:53

The key factors are going to vary from person to person. You'll ultimately have to decide for yourself what's more important. As far as warmth goes, that's going to depend on where you are going, and how well your body handles the cold.

Just like you noticed, sleeping bags fall into one of those classic triangle patterns with the other factors you listed: Cheap, Warm, Lightweight/small size - Pick two.

In my opinion, I believe that the process of selection for a sleeping bag goes material, then warmth, then price.

Material choice is basically down vs synthetic. For a down and synthetic sleeping bag with equivalent ratings, the down bags will generally be more expensive, lighter weight, and pack smaller. If you are backpacking in places it can get below freezing, down seems to be the only suitable choice.

Generally, down is superior in all aspects except for two: it's more expensive, and if it gets wet, it's pretty much completely useless until it dries. Synthetic bags will still keep you warm if they are wet, while after frosty night in a wet down sleeping bag, you might never wake up.

Personally, I find the packed volume to be more important than the weight difference. A down sleeping bag is often smaller than it is lighter relative to a similar synthetic. I have both a synthetic and down sleeping bag. My synthetic weights 2 kg, while the down sleeping bag weighs about 1.3kg. The synthetic bag cost a hair over half as much as the down, $139 on sale vs $260. However, the synthetic bag takes up a massive 35L packed, nearly half my pack! The down bag on the other hand, I can cram into a 8 liter compression sack.

However, there are synthetic bags that can be more reasonably compressed, but then they approach the cost of the down bags.

Once you have a material choice, generally the colder you go, or the smaller you go, the more expensive it will be. You'll have to decide where the tradeoff is between size or warmth and price.

For the OP specifically I think for the 35-45 range, you should be able to find a suitable synthetic sleeping bag that doesn't occupy too much of your pack. I am heavily biased from going on many trips where getting down to 10-30F is fairly frequent.

And of course, you can also buy yourself 5-10 degrees F or so of extra warmth with a sleeping bag liner, along with the added bonus that they protect your sleeping bag from getting filthy.

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You mentioned that 35 L is pretty huge and takes up half your pack. Is there a rule of thumb about what percentage of your pack should be used for your sleeping bag? –  Mike Deck Jan 3 '13 at 16:46
2  
Not as far as I know of. Obviously having a bigger pack will mean you can get away with a larger sleeping bag. The required ratio will depend on how much other stuff you have. I imagine the ideal size for everyone is perpetually "smaller than my current sleeping bag". –  whatsisname Jan 4 '13 at 5:11

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