Ahhh... the bivouac. Long hours of fitfull sleep on lumpy ice with a bivy bag intent on suffocation. Waking up every 15 minutes wishing for dawn to arrive, yet when it does it requires a masochist to crawl out and put the billy on.

Open bivouac on the Ranfurly Glacier

Indeed the bivouac is a nasty beast. Why would anyone choose to write an article to champion its merits and advance its cause? Here's a worse thought... what if an article entitled The Art of the Bivouac convinced you the bivouac was the right way to go? Perhaps you should stop reading now. Ignorance is bliss. Mountain huts and bunks and big fat sleeping bags are bliss.

The Purpose

There are three reasons to bivouac on a mountain. First, it is an emergency situation, or at least an unplanned night out on the mountain. Second, it is planned because the route is too long to climb in a single day. Third, it is a "tactically" planned bivouac (I can't think of a better word).

And it is these tactical bivouacs the author would like to encourage. So I'll give some examples.

The "tactic" is often to bivy and wait for problematic conditions to change. We can halt a climb in the heat of the day and wait for snow conditions to improve as evening approaches. Or if close to summitting, we can sit out bad weather even without bivouac gear. Staunch stuff that elevates a climber to legend status. Obviously you don't want to screw this one up... sometimes it is better to just back off and turn up at work on Monday as the boss was promised.

The "tactic" can be to push harder when obstacles arise. This may not sit comfortably with many, but most climbers turn around when faced with unexpected difficulties when they don't need to. If we get delayed by difficult climbing, crevasses, a poor freeze, a change of route then consider pushing on with a high bivouac. With knowledge of how to bivouac using minimal gear all those peaks we once missed out on by a couple of hundred metres become successful summits.

A 5-hour delay - fixing and jugging a problematic crevasse, Balfour Glacier

Yet the tactical bivouac can be a totally planned event. Approaching fine-weather windows don't always correspond to the conventional start and finish times of our climb. We may need to start climbing as soon as the clearance arrives, even if that is 6 o'clock in the afternoon. Or how about linking multiple routes on the same or adjacent mountains, perhaps climbing five routes in three days of good weather? No-one ever seems to try this. It does take some skill since although anyone can go light for one bivouac, it's a bit harder to fit four days supplies in a 30-litre climbing pack in the middle of winter.

Right! All fine in theory but the practical problems are obvious. We are either going to be carrying monster packs with sleeping bags, roll mats, stoves and bivy bags or we are going to experience freezing nights without sleep and be wrecked for the next day. I'm sure you've all heard the saying, that a climber who carries bivy gear will bivy.

So somehow we need to get smarter about this bivouac concept.

And by some incredible good fortune that is what this article is about.

Like all good boy scouts and girl guides we start with looking at our gear.

Sleeping Bags - Temperature Ratings

The question is, will Company A's -15 degree bag really keep me warm at -15 degrees? The manufacurers themselves acknowledge there are many other factors involved such as a person's food and water intake, exhaustion, type of sleeping mat, metabolism, clothes and so on.

But all of these are insignificant compared to one overwhelming factor - the temperature of the air the person is breathing.

Prime real estate. View from bivouac on south face of Mt Cook

What do I mean? The temperature of the air we breathe is -15 degrees, right? No.

The air you breath out is warmer than -15 degrees because it was warmed by your body. If this warm air simply escapes into the night air you are required to breath air at -15 degrees again. However if you can trap the warm air around your head then you are breathing air that is effectively preheated.

Does it make much of a difference? It makes all the difference! In fact no sleeping bag should have a temperature rating lower than about -10 degrees because it is not possible to sleep while air this cold is being sucked into the core of your body. Some of the more "scientific" temperature rating measurements made by manufacturers use metal bodies within the bags to measure heat loss. Yet these bodies really require vacuum cleaners as their internal organs to be representative.

On the other hand, if you can trap the air around the head, then ridiculously light-weight bags can be used in very cold conditions. Believe it or not, you can sleep perfectly well at -40 degrees using a +5 degree rated bag with a well designed bivy bag without needing a down jacket or any other high insulating clothing.

We will discuss methods of air trapping throughout the article, but this same principle is why you naturally tuck your head in and try to breath air from inside the sleeping bag when feeling cold.

Sleeping Bags - Synthetic vs Down

A full discussion of sleeping bag design would bore even me so we'll only touch on the one aspect most relevant to bivouacing - the synthetic versus down debate.

First we need to know exactly what we are comparing. Lets start with synthetic bags. We are looking at the high performance bags retailing at $350 and above. We are not interested in the cheaper $100 - $200 bags most manufacturers produce. The only high performance synthetics to be found in New Zealand are Polarguard 3D for warmer bags and Softie for lighter bags. For the moment we'll only look at the Polarguard 3D bags since they are of more interest to most climbers.

Now for the down bags. In surveying the down market we must realise that the performance of the bag is dependent on the quality of the down. Higher quality down lofts more and traps more air for insulation. The measurement of loft is the "fill rating", with lower end down about 600 and higher end down pushing over 900.

Of course you can make a bag with 600-fill as warm as a 900-fill bag, you just need more down to do it, which adds weight and bulk. Be careful to note whether a manufacturer is referring to an average or minimum fill rating.

How are we going to compare performance between synthetic and down? It is very simple. Take a catalogue and compare the weight and pack size of a synthetic and a down bag with the same temperature rating. Since the bags were made by the same manufacturer, using the same shell materials, hood design, bag dimensions and of course using the same scientific method to determine temperature rating, then the comparison is completely justified. For instance,

looking at Marmot's -18 degree bags we find,

Polarguard 3D: 1786g Down 600-fill: 1704g Down 800-fill: 1533g

What are the results? In the case of Polarguard 3D the synthetic weighs about as much as an equivalent bag made of 600-fill down (but is a bit bulkier). As we'd expect, 800-fill down bag is significantly lighter and more compact. Note however that a 800-fill bag is not within the budget of all climbers and most bags sold in New Zealand are 600 to 750-fill. I'm not even going to include the statistics for a 900-fill bag because you won't be able to afford one.

So even 600-fill has slight avantages over a top of the line synthetic. If you spend your two week holiday based at Plateau Hut and your sleeping bag never leaves the bunk except for when you walk out, then down is the way to go (except a top line synthetic is still cheaper than a down bag).

But what happens when we step into the real world? The real world of sleeping in the mountains. Do synthetics rate any better?

Most climbers know that when the &#$% really hits, and they are forced to sit out a serious bivouac, they would much rather be in a synthetic. A Polarguard 3D bag retains 60% of its warmth when dripping wet. A down bag retains next to nothing. No water resistant shell will keep the water out for even the first night, let alone several. In practice, most climbers find it difficult to keep the bag dry even within a bivy bag.

Okay, you already knew this. But you aren't planning on getting caught out and you'll probably survive anyway, so is it worth lugging around a (slightly) heavier and bulkier bag? Only if there are other performance benefits. And there are a couple.

For the first we need to revisit the idea of loft. As you know - the more loft, the more trapped air, the more warmth. The problem with down is that it lofts slowly. After being stuffed into a stuff sack for the last couple of days it takes a long time for the down to uncrumple and for the full loft to be achieved. All those plump bags in the store are plump because they have been lying on the rack for the last 12 months. They have signicantly less warmth when pulled out of their stuff sacks each night.

Synthetics spring out of their sacks. They have instant maximum warmth. Remember, those temperature ratings are for fully lofted insulation - so synthetics start to look better.

For the second advantage of synthetics we need to revisit water again. But not in an emergency sense, just in everyday (night) use. How damp does your sleeping bag get during a good bivouac?

The major issue is that your breath releases a lot of moisture. If you are in cold conditions you must use a bivy bag, close the hood and trap expelled air. All the moisture you breathe out gets soaked up by your sleeping bag. Each night the situation compounds itself.

We already know a synthetic is less affected by moisture. Synthetics also dry faster. As you'd expect, when manufacturers measure the temperature ratings of sleeping bags they use ultra-dry laboratory environments.

(Ever tried washing your down bag? It's usually something we only do once after spending three weeks of unclumping and drying the down. It is interesting to note manufactures say down bags last longer than synthetics - but in practice this is not true because we never wash down bags.)

So who is the winner - the synthetic bag or the down bag? Of course every situation is a bit different and perhaps there is no overall winner. However, if you want to push things to the limit and use ultra-lightweight gear and methods of heat capture (which this article is really all about), then you must go synthetic. Down simply doesn't work.

If you do choose to go this way then there is information about high performance synthetics at the end of the article since your local store won't be able to give you much advice.

But now we turn to the most crucial piece of equipment...

The Bivy Bag

Fairydown bivy bag featuring raised hood and breathing vent

The basics: bivy bags are like a rain jacket for your sleeping bag so you can sleep out in any conditions without needing a tent or snowcave. They are similar to your own jacket as they are constructed with waterproof/breathable fabrics and taped seams. Hence they cost as much as a jacket.

The choice of bivy bag is dependent on your style of climbing.

If you only want something for emergencies then you want the most lightweight bag possible. 600 grams is typical but 300 grams is possible. You are not going to be able to sleep with these bags fully zipped because having material flat on your face is nightmarishly claustraphobic. But it will save your life in an emergency situation. They are also suitable for use without zipping the hood closed in good weather, snow caves or leaky tents.

What about using a plastic pack liner? It is likely to save your life but not much use for anything else since the material needs to be breathable for you to stay dry.

If you want to be able to sleep well in poor weather or use the bag to trap warm air around your head then you are after something with more design.

Most importantly the hood needs to be lifted off the face. The best and lightest method is a thin, flexible plastic rod that fits into a sleave and gives shape to the hood.

This reduces claustraphobia dramaticly. But to improve sleeping conditions further the moisture from your breath must be removed also, since the breathability of the fabric can't compete with your lungs.

One nice feature is a water absorbing felt-like material lining the inside of the fabric, such as Bibler's Toddtex fabric. It works surprisingly well, further reducing the claustraphobia.

The ultimate though, is an air vent located on the chest. By adjusting air flow the claustraphobia is almost totally eliminated and comfortable sleep is achieved in any conditions from torrential rain to sleeping on top of Mt Tasman without a sleeping bag. The vent is a much better mechanism than simply creating an air gap with the hood zip.

The type of breathable material used in construction is not as crucial as these features. Although it is possible to find bags constructed of ultra-breathable fabrics, air vents are the most effective way of reducing humidity and eliminating claustraphobia.

What other considerations are there when purchasing a bivy bag?

Ensure the bag is the right size for you. Size will depend on your own dimensions plus the arrangement of sleeping mat, sleeping bag, sleeping bag liners, a jacket for a pillow, storage of water bottles, headlamp and possibly boots (if leather). A longer zip improves entry and exit to this establishment.

All these features are at the expense of additional weight, with a fully kitted bag pushing 800 grams. But fabric thickness is also a factor here. A simple bivy bag made of heavy fabric can weigh more than a featured bag made of lighter fabrics (which they always are). Durability isn't a major concern in the alpine environment. Obviously the base of the bag is most susceptible to abrasion and some manufacturers use a non-breathable tough plastic for this section. Breathability isn't required for the base of the bag.

Sleeping Mats

Summer rock bivouac, Nuns Veil

Surprisingly, $10 closed cell foam mats are warmer than $200 inflatable air mats.

Not surprisingly, air mats are a lot more comfortable, especially when sleeping on your side. If the bivy is going to be a cold one you will spend most of your time in the feotal position.

A further advantage of the cheap closed cell foam is you can cut it into a half length to cover from your shoulders to your buttocks. This saves weight. Your jacket and overtrousers can be stuffed under your legs and you have a fleece jacket-pillow for your head. If you are pushing the limits and need to wear most of your insulating clothing then wear your helmet to keep your head off the snow. There is no great advantage to wearing your waterproof clothing and you'll end up getting quite damp. If you are wearing your inner boots you won't need anything under you feet.

An issue with air mats is they need to be inside the bivy bag with you (to protect them from rain and snow). This does limit your ability to curl up when cold.

In an emergency situation you may have a bivy bag but no mat. A surprisingly comfortable solution is to sleep on your climbing ropes. Unfortunately it requires three ropes each for a truelly blissful sleep. Another option is to lie on an empty pack but it will be a long cold night. Without a proper mat some part of the body tends to be resting on the ice which tends to ruin the night's sleep.

Stove

If the bivouac is planned it is usually a mistake to leave the stove behind to save weight. It is amazing how much water the body uses even when asleep and the following day is going to be a hard one if you start with only a litre or two in your pack.

If it is a single bivouac then taking a small gas burner is a weight advantage over a liquid stove. For mulitple bivouacs the efficient liquid fuels are more beneficial.

Although hot meals are tremendous for the soul they require more fuel, a pot, bowl and eating utensils. For a true lightweight bivouac carry ready to eat food such as nuts and use the stove only for melting water. A small steel cup with a lid can be used instead of a pot. Heating several small quantities of water is more fuel efficient than one large quantity.

That's enough about the gear, how do we actually bivouac?

How Do We Actually Bivouac?

Of course the answer to this question was mostly covered in discussing the equipment above. That's the thing about mountaineering - technique is never divorced from equipment. This section covers practices not so far discussed.

There is no substitute for getting out there and having bloody awful bivouacs. Try using sleeping bags that are too light and a selection of bivy bags on lesser climbs. It is the only way of finding out what you can get away with.

But on to a few ideas we can cover from the warmth of our living rooms...

Idea 1: There are other methods of capturing heat around the head. Since we are not going to build a snowcave we could look for the next best thing, a small crevasse. If the slot is covered so the entrance is from the side it is effectively a ready made snowcave. The smaller the crevasse, the more it will heat up.

A partial snow cave to cover the head, Hooker Valley in winter

Such a tube-like crevasse is not always available. So the next option is to dig a small cave for the head to lie in. This can be done in a crevasse or in the open. For instance, a cave can be cut into a snow bank for the head and the body can stick out into the elements. It is remarkable how still the air in the cave is while a full gale is blowing outside (provided the wind direction is right!). Similarly, on a flat plateau a small snow mound can be built, or on a ridge rock walls and packs work well.

The whole point is this. We don't have to build entire snowcaves, snow mounds or shelters. Just cover the head. So if our bivy bag isn't great for zipping closed over the face we can leave it open and still sleep in cold, windy or wet conditions.

Idea 2: A lot of climbing is better at night. A good freeze, less dehydration, less avalanches and concrete snowbridges. On the other hand sleeping is more suited to daytime since it's warmer. So put two and two together and consider climbing at night and bivouacing during the day. You don't need much gear to sleep during the day. This works brilliantly for multiday climbs. Works even better during the depths of winter because there is so little daylight to use anyway. Works less well for highly technical routes which require some visibility and lots of hanging around belaying. Idea 3: Not rocket science and you already know this but take lots of hats and balaclavas. They are the best warmth-for-weight items you can carry. According to medical theory you will sleep warmer if you are well fed and watered because digestion releases heat. Apparently exhaustion makes you more susceptible to the cold but I never find it hard to drop off when I've been on the go for 24 hours.

What Is Possible?

An emergency snow hole without bivy gear, winter on Mt Walter

With practice it is amazing what you can get away with.

In summer on top of the big mountains sleep is possible with just a roll mat and well-designed bivy bag. A light 2-season sleeping bag will make things quite cosy.

In winter on top of the big mountains the roll mat / bivy bag combo will ensure survival but a fitful sleep. Even lying on your pack in a small snow hole will get you through the night. A 2-season sleeping bag should provide a comfortable night.

Foam roll mat, bivouac bag, 2-season sleeping bag, stove, fuel bottle and small pot can be carried using a 30-litre pack with enough food for several days' climbing. All your climbing gear can hang off your harness.

However, it is true to say practice often means bad nights in the mountains wishing you were somewhere else!

So, I wish you pleasant dreams, starry nights and here is an appendix on synthetic sleeping bags to round things off nicely.

Appendix - Synthetic Sleeping Bags

So you're toying with the idea of going synthetic? It's a difficult step to take because you're trusting one guy's advice over most of the industry's wisdom. You aren't going to be able to test drive the product either. And to top things off no-one will be able to tell you squat about performance synthetics.

At least we can address that last issue here.

But I have to start by saying it is impossible to make this section scientific. We are dealing with different companies using different materials and different measuring sticks and the data is just not there in the public domain, even when repeatedly requested. These are the author's own findings and no claims are made with documented science. Hopefully it will provide you with a starting point and give an idea of what to consider. It will all be out of date in a year anyway.

In New Zealand there are two high performance synthetic fills that compete favourably with down.

Polarguard 3D is used by both Marmot and Mountain Hardware and their products are available in this country. However, there is a noticable difference between them. They aren't made the same, don't feel the same and don't pack the same. And I haven't been able to find out why. I do not wish to be controversial (or sued) so I will leave it to you to find out which is which. I shall simply use the names Company A and Company B, in no particular order.

Simply, Company A's bags are very bulky. It is not possible to pack these to a managable size even with compression sacks. Company B's bags are definitely spring loaded but a good compression sack and muscle power does reduce them to down-like proportions. (Compression sacks are far more important (essential even) for Polarguard 3D bags than down bags).

Both companies also use Polarguard Delta, which has performance benefits over 3D of about 10%, but is significantly more expensive and the range is limited.

The other synthetic fill is Hardi's Softie material used exclusively by Snugpak. A strange material that insulates without dramatic lofting. This synthetic can only be beaten by 900-fill down in light-weight sleeping bags. For instance, sampling 0-degree (minimum) rated sleeping bags,

Snugpak Merlin 3: 750g
Marmot 600-fill down: 880g
Marmot 800-fill down: 852g

and there are no compactability issues with this synthetic. I know, I know, I shouldn't compare temperature ratings from different brands (since they use different measuring sticks for temperature ratings), however from personal experience I have found the Merlin 3 to be lighter and more compactable than any 3-season down bag I have used.

This is all at the light end of the market. As we move to warmer sleeping bags the Softie material loses its advantages and both down and Polarguard 3D are superior. This statement is implied from technical data given by Snugpak but I can't verify it because the Merlin 3 is the warmest Snugpak bag available in New Zealand. Since Snugpak do not make down bags no direct comparison can be made.

All this may surprise us. We'd expect an insulation to be superior / inferior irrespective of whether we were discussing summer or deep winter bags. However, rarely are sleeping bag specifications linear. This is due partly to different construction, partly to different thermal properties and partly to added features like reflective material woven into synthetic fabrics. So we can't simply end the debate by taking samples and attaching a thermometer. Similarly the down versus Polarguard 3D comparisons are different for different temperatures, even if the bags are made by the same manufacturers.