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I'm planning to buy my first sleeping bag. I'm a newbie who's never had a sleeping bag before. I'd like to know about your experience with using synthetic vs down bags for outdoor use (under the sky). I've read you have to be careful using down bags outdoors and watch out for moisture (by using a bivvy sack) and that it's more difficult to take care of it as opposed to a synthetic one.

Budget is not a problem, I am willing to invest in a down bag, but I'm wondering whether it's a good choice for me as a newbie backpacker who is planning to go on weekend (or longer) trips outdoors.

I would prefer a down bag, so I would prefer to hear if someone is experienced in using down bag outdoors (sleeping under the sky). I heard that moisture can make the sleeping bag less effective, and I am worried if permanent loss of insulation properties can happen if it is exposed to morning dew.

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    it's your first time sleeping outdoors and you plan on starting with just a bivy bag? Most people use a tent or a tarp, at least.
    – njzk2
    Mar 19 at 21:47
  • @njzk2 I've slept under the sky couple of times, but with my friend's bag (which was synthetic). I'm asking whether a down bag is suitable for outdoor use without a tent and what to look out for. Mar 19 at 23:10
  • Ducks sleep under the sky all the time, their feathers are made for it, just make sure your bag is dry before you pack it away.
    – ShemSeger
    Mar 23 at 16:54
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Down bags are an excellent choice for backpacking/hiking because of the volume and weight considerations. For two comparable temperature range bags, down will be at least 50% smaller when packed and a similar amount lighter than the artificial fill fiber. These two considerations are often significant when out in the woods -- the less weight and volume you have to carry on your back, the better your day will be.

The downsides to down are that a wet down bag will not keep you warm and they provide no or very minimal insulation/padding on the underside so you have to do 2 things -- carry a sleeping mat for insulation/protection from wet ground and keep your bag dry. Modern high quality down bags (e.g. Rab, Patagonia) are usually made with a water resistant/repellent and breathable fabric to help keep the bag dry. These fabrics have a dual role in protecting the bag from dirt and from dampness, making the bag easier to clean externally and keeping it dry.

Breathable and waterproof/resistant fabric alone is not enough to keep you dry if sleeping on damp ground or in the rain/snow, but it is enough to deal with a light dew and perspiration from your body. For protection from damp ground, your sleeping mat will take care of this. For rain or other precipitation you need to have some protection from the elements, be it a tent, tarp, or bivvy bag.

Generally the moisture from your body and the dampness from a light dew etc is not enough to cause permanent loss of insulation in the bag, unless the down becomes saturated and clumps together when drying. A light dampness can be easily dried over a handy branch and will not affect the performance of your bag. If your bag does get wet (more than damp) and do need to dry your bag, it is best to be able to do this in a dryer at home with a couple of clean tennis balls thrown in to help break up any down clumps. At the end of each trip you should make sure that you properly air out your bag by turning it inside out and hanging it up to dry for a day or two, preferably in a sunny spot. It should also be stored in as open a state as possible to prevent the down being compressed and losing insulation thereby.

Another reason to carry a second protective layer is that a sealed shelter like a bivvy bag or tent is that this adds to the insulation level of your bag, generally adding about 3-5 degrees Celsius (~6-10 F) to your temperature range, though your mileage may vary depending on the type of tent and conditions where you are camping. A tent will also help keep your bag and mat clean, which help with making your bag last longer.

One addition to your sleeping bag that I have found very useful is a liner that goes inside your bag when sleeping. This gathers the sweat/dirt off your body rather than it all ending up in the bag itself. They also add a small bit of extra insulation, though this depends on the material they are made from. Liners can be very compact and light if made of silk, so only add a minimal volume and weight to your pack.

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    Liners are definitely worth it. With care the outside of a bag should stay clean, but humans are dirty things especially in the wilds, so the inside will suffer without something. Sleeping bags may be washable,but it's still not something you want to do often. Plus the liner gives you more options for a wide range of temperatures in the same trip
    – Chris H
    Mar 20 at 8:53
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If it's going to rain on you, then you want some way of keeping the rain off, or you're going to be miserable. The method of keeping the rain off can be a tarp, a tent, or a bivvy sack. If I'm going backpacking in Southern California, and the weather forecast is for clear skies, then I wouldn't bring any of these things.

If I expect mosquitoes to be very thick where I'm camping, then I want a tent. In cold and windy conditions, a tent keeps off the wind. If the ground is muddy and wet, a tent will keep you dry.

A tarp is an excellent ultralight option, especially if you don't expect large amounts of bad weather, but it requires quite a bit of practice to learn to set it up, and every location is different. When it's windy, tarps tend to flap all night and make noise. If the ground is wet, you'll also want a ground tarp, although this can be a very lightweight piece of plastic.

A bivvy sack is a good option if you're mountaineering and you want a life-saving way of keeping rain and snow off in case of an emergency bivouac, but you don't want to carry a tent. People I know who have slept in bivvy sacks have generally never said anything good about the experience. Moisture tends to condense inside the bivvy sack from your own breath and perspiration, so you end up wet. If it's raining, then rain tends to get on your head no matter what you do.

In the relatively dry conditions here in California, I generally use a down bag and bring a tarp along in case of rain. Once in a while, when I've camped near a creek or in foggy weather, I've woken up in the morning to find the bag damp on the outside from condensation. This is not a huge problem. The bag will still retain its insulating ability when the only moisture on it is this type of condensation.

Down sleeping bags are much lighter and smaller than synthetic ones for the same amount of insulation. The main reason for using a synthetic bag is if you can't afford a down one.

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  • Plenty of people do use bivvy bags of some sort routinely, but expensive ones, sometimes combined with a small tarp to optimise shelter vs ventilation. My lightweight setup uses a tarp, but bivvy tents were an appealing option - tiny tents with a single pole at the head end,or even just a cord from a branch overhead
    – Chris H
    Mar 20 at 8:50
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I can't compare down with synthetic, because we have used only down in all our 40+ years of backpacking -- and never had to replace the bags. That is, our down bags are more than 40 years old. They are from North Face.

Although we always carried a tent, we slept outside the tent whenever the weather permitted.

Perhaps our best test of the bags was when we were camped (no tent) beside the Tuolumne River and we woke up to find our bags covered with thick frost. Total Surprise! (This was at 18 degrees F. We always carry a thermometer.)

There is another caveat: Most of our backpackpacking has been high in the Sierra, where the air is usually dry. The moisture condensed on our bags was usually from our bodies, and whatever moisture there was dried very quickly in the morning. That is, we never had to crawl into anything but a completely dry bag at night.

To summarize: If it is snowing or raining or drizzling or damp and raw, you will probably elect to use the tent; if it is not, atmospheric moisture (in the Sierras and Rockies) will not be a problem sleeping under the stars.

Of course, if your tent leaks or condensation inside the tent rains on you, a synthetic bag may be better. We have experienced both with the down bags, and always cobbled together a solution with tape and/or the spare ground cloth.

As for care: Even I am surprised that we have usuable 40 year old bags. We took good care of them, but did not obsess over care. We never stuffed them damp, if only because we are slow getting started in the morning. We shake them out daily, and air them several times in the course of a two week trip. We always stored them between trips loose in a large closet. We dry clean them perhaps every 3 or 4 years at a reputable dry-cleaner. We repaired tiny rips quickly with tape. (And we kept the cats away from them.)

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    The flip side for those of us that live in temperate maritime climates is that there's almost always dampness around - if not rain then dew or condensation inside a tent (which you're using because there's a fair chance of overnight rain). My last night away, in the so called height of summer was at about 400m altitude, above the cloud base. Under a tarp everything was damp on the surface, but my synthetic bag was fine. usage conditions are important, In other words
    – Chris H
    Mar 20 at 15:00

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