Personal Metabolism

People react differently to cold. If you know from experience that you feel it more than most (you tend to sleep cold or you get cold hands/feet very easily), then it’s worth taking this into account when choosing your insulated gear.

For this reason we have whenever possible included a warmer item among the list of choices, beyond the 'typical' specifications. And if you feel that even this may not be enough, you can switch to the gear list and choose something even warmer. Hands and feet are often the first parts to feel cold. So even for destinations where you might not think of taking them, such as Elbrus or Kilimanjaro, we have included Down Mitts and Down Boots as optional 'comfort' items. They weigh very little and can contribute a lot.

Windchill

Wind is a constant feature of high mountains, and wind allied to cold can be a killer. Wind doesn’t lower the actual temperature - that is not what windchill means. Instead it strips away some of our defences and increases the effect of cold on us. The higher the windspeed the faster it works.

Notes to Table:

1. It is the combination of cold and wind which is so deadly. You can see from the table that at 0C a 10mph wind will drop the windchill temperature by 6 degrees: at –30°C the same windspeed will drop it by 14 degrees.
2. The first big onset of windchill occurs at quite low windspeeds. The first 10mph has far more effect than increases beyond this level. Of course higher windspeeds do remove heat even faster, but at 40mph and above you are moving into a situation where the wind has other major physical and psychological effects beyond windchill.

The windchill figures in the Table, like the ones you hear quoted in the weather forecast, are for bare skin. They are directly useful to warn of potential frostbite to hands or face. Useful also as general indicators, although they do not apply in this simple form to areas of the body protected by windproof clothing. Everyone knows how it feels to be out in a cold wind in porous clothing like fleece: not frostbite territory, but very different from a still day. Put on a windproof garment and the change is remarkable. You’ll still be losing heat, but very much less from the shielded parts of your body.

The Drishell and Tempest outers on all PHD’s mountain and expedition gear, even the sleeping bags, are 100% windproof, unlike some fabrics which merely look it. You can have full confidence that when you don’t have a shell garment over the top of your down gear, you are still well protected against the most insidious danger of them all. This applies even more to the hands, which are often exposed to the wind and liable to frostbite. On many expeditions windproof mitts are a must.

On the highest peaks like Everest the question often comes up of whether it is worthwhile taking a onepiece windsuit. Some do, some don’t. If the outers of your down gear are all 100% windproof (like PHD), then the main purposes of the windsuit are:

1. To cover fleece etc lower down the mountain, when the down gear is still in your sac.
2. To cover a split system (down jacket and trousers as opposed to a onepiece down suit) high up to add an extra bit of security.

People have also taken windsuits to wear over the top of windproof down suits as a kind of double security. Just note that windsuits are sized differently to cover fleece or down.

In Antarctica shell gear is often used to combat cold wind when the user is working hard and generating a lot of heat. This has led to the popularity of Ventile, a highly breathable cotton, which is not totally windproof, but has a dense enough weave to be effective in these conditions.

Sleeping Bag Zips

Some PHD sleeping bags have full length zips as standard. On the rest it is an option, so the choice is yours, whether to go for short or long (or none). Here are the simple basics for deciding:

Full zips:

1. Versatility. Full zips can be used over a wider range of temperatures e.g on a trek that includes low and high levels.
2. Future versatility. If your next destination is going to be less cold or if you want to go camping somewhere closer to home like UK, a full zip can make a warm bag more widely useful.
3. Joining. Full zip bags can be zipped together.

Short Zips

1. Weight & Bulk. Short zips are lighter and pack smaller. A full zip & draft tube is about 85gm (3oz) heavier than the short equivalent.
2. Simplicity. Short zips are easy to use and in the rare event of a zip failure the consequences are less serious (particularly true of the Xero bag where the zip is backed by a down-filled expansion gusset)

No zips

1. The standard design on our lightest bags with open hoods. The simplest/lightest system which is a must for adventure racers.

Summary

Treks - Full Zip option is nearly always the best choice

High Mountain & Polar Expeditions -- There is much to be said for Short Zips. But what about future trips?

Ultralight - No Zip is the first choice

Down vs. Synthetic

For anyone allergic to down the choice of insulation is simple – you need synthetic. For everyone else whether to opt for down or synthetic remains a question.

The arguments can be summed up quite simply.

For Down

1. Down is much warmer weight for weight (about double)
2. Down compresses better
3. Down lasts longer

For Synthetic

1. Synthetic performs better when wet and dries quicker
2. Synthetic is cheaper

From these basic points it is clear that if you are going somewhere really wet, you should seriously consider synthetic. Anywhere else down has all the advantages. For a fuller discussion of this topic, see Technical Briefings.

Note: In the the cold humid conditions of the Arctic there is a danger that the moisture coming from the inside (from you) will freeze inside your insulation. This is equally true, whether the insulation is down or synthetic, and has to be countered by the efficient use of Vapour Barriers.

Other trips

The main aim is to get the right gear for your present destination. At the same time, if you are considering more trips in the future, it is worth taking them into account. While it is simpler to take one trip at a time, it may save money if you look ahead.

Going warmer: Look at the note on Sleeping Bag Zips. A full zip makes your mountain bag usable in the valley too.

Going colder: If your next destination is likely to be colder, then check it out on this website and see what gear is recommended. You may find that there’s an overlap with your current destination, so you could cover for a colder trip without adding too much to weight and price.

For example: The Diamir 900 sleeping bag is listed as a 'warm' choice for Kilimanjaro: it is also named as a good choice for Aconcagua (a colder mountain) if that is in your sights.

Even if you are not going to any of our listed destinations, the same applies to any two trips which are not too far apart in temperature - just look at the gear tables and see if there are items which will cover you for both. PHD gear is extremely light and quite often you will find that you can cover for a future colder trip as well as the current one and still end up with a remarkably light load.

One-piece Down Suit versus Jacket and Salopettes/Trousers

The Poles and the 8000m peaks often bring up the choice between a one-piece down suit and the combination of down jacket and salopettes (or trousers). These are extreme environments, and if in doubt it is always worth asking advice from people who have already been to your destination.

To help you here is a summary of the main points involved.

A simple summary like this is not much help, we know. But it may be worth having the basic pros and cons staring you in the face while you work out which way to go.

When looking at Shell gear the reasons for considering a one-piece windsuit are quite different. Please look at the footnote in the Windchill section.

PHD Sizing - Clothing

The PHD Sizing Chart below is based on measurements without clothing, exactly the way you would buy a shirt, a sweater or a pair of trousers. A 42" (107cm) chest means that your bare chest uninflated measures 42". Inside Arm is measured from armpit to wrist-bone and Inside Leg from crutch to ankle bone. If you find that you fall between (or across) these sizings, please contact us and we will quote you for modifications needed. And if you are supplying us with your measurements, it is always useful for us to know your height, even when you are only buying a jacket.

Allowances

• Down Jackets, Pullovers, Vests, Down Suits: sized to fit over thermal underwear and fleece.
• Down Trousers and Salopettes: sized to fit over thermal underwear and/or climbing trousers.
• Shell Jackets: sized to fit over thermal underwear and fleece or light down clothing (e.g. Minimus Jkt): to cover thick down clothing, go up one size.
• Shell Trousers and Salopettes: sized to fit over thermal underwear and/or outdoor trousers.
• Shell Suits: D-type suits will fit over down clothing of the same named size: F-type suits will only fit over thermals and fleece.

PHD Sizing - Sleeping Bags

The measurements in the Sleeping Bag chart below are personal body measurements (The figures quoted for sleeping bag dimensions vary widely in the way they are calculated and lead to some manufacturers quoting figures apparently suited to giants over 7 feet (213cm) tall).

Temperature Ratings

It is theoretically possible to give estimates for the insulation needed at different temperatures. At 0°C you might need 5cm of insulation, at -20°C 7cm, and so on. Or the figures might be quoted in units of thermal insulation, roughly 10 Togs (6.5 Clos) for 0°C. But quoted baldly like this the figures have no meaning. They have first to relate to what you are doing, your activity level, and even then they are for such 'idealised' conditions, ignoring wind, humidity, personal physiology and many other important factors, that they bear little relation to the real world. Each element of reality which is added to the equation multiplies the complexity of the answer, until it becomes apparent that temperature ratings are very approximate guides at best.

Like many manufacturers of insulated gear we would prefer not to give blanket ratings for our products. It would be far more accurate to talk to every customer about their particular needs. That is impractical, even for a small company like PHD, and yet customers still want some sort of guidelines. So there is little choice except to join the process and quote ratings. What follows is a brief explanation of how we go about it and of what value you can place on the results.

Sleeping Bags

Sleeping bags are the easiest. Even here ratings are necessarily hedged about with all sorts of conditions (often unstated), but they are not complete nonsense.

You have a fixed activity (hopefully you're sleeping) and you're probably in shelter, even if it's just a bivvy sac. That cuts out two of the major factors which bedevil ratings, activity levels and the wind. But it still leaves a long list of things, starting with your personal metabolism and going on to food intake, clothing, ground insulation, humidity, altitude, fitness, etc. The combination of some of these can seriously alter any figures.

To confuse the picture even further, there are certain psychological factors which often come into play. Person A feels the cold to exactly the same degree physically as person B: but A sees himself as the hardy type and puts up happily with a skin temperature which B finds unacceptable. Similar situations can arise from experience also, if A is a very practised outdoor person and is not fazed by the familiar sensation of cold, while newcomer B finds it unpleasant and a bit scary.

So what to do? How can we find a way to quote meaningful ratings? Some people try to solve it by being more precise and quoting two (or more) temperature figures, 'comfort', 'extreme', etc. Others go broader and vaguer and use the 'season' rating system. But precise or vague, no system can cover for all the possible variants mentioned above.

So at PHD, knowing we can't eliminate the uncertainties, we have tried to keep it simple. What we quote for each of our bags is: a single Typical Operating Temperature (TOT) at which you should be able to get a night's sleep under normal circumstances.

By 'normal' we mean:

• you're in shelter
• you have eaten normally
• you have sufficient ground insulation
• your bag is dry
• you're not a 'cold sleeper'
• you're wearing clothing appropriate to the conditions: below 0C (32F) we would expect anyone to wear at least thin thermal underwear, below -25°C (-13F) at least thick thermals.

And while we're describing what's normal, we should add that if you're an experienced 'hardy' type, you can probably take the bags below their quoted temperatures by about 5°C (9F).

This seems like a lot of words to finish up with one fairly shaky statistic. Please take it for what it's worth, a starting point which becomes much more valuable when fleshed out by your own experience, or by experienced advice from others. If you're still in doubt about your choice, contact us and we'll try to help.

Clothing

The difficulty of establishing meaningful temperature ratings for clothing is much greater than for sleeping bags. So much so that most manufacturers sensibly don't attempt it.

Then why do we quote temperatures in our Clothing Comparison Guide? Would it not be less misleading to omit them altogether? Our feeling is that as long as we make it clear what kind of indicator you are looking at, then there is some value in a broad classification to simplify choice. This is how we go about it.

Besides actual ambient temperature there are two factors above all which affect our insulation requirements: our activity level and the wind.

Wind

Wind we have mentioned elsewhere under 'Windchill'. All PHD clothing (except the ultralight Minimus clothing and our fleece items) has a 100% windblock outer which reduces this factor to manageable proportions, although you will still need to take great care with exposed areas such as face and hands. And of course very high wind speeds will always intensify the effect of low temperatures to a point where it becomes more a question of seeking shelter than of clothing ratings.

Activity Level

It is the other major variable, activity level, which we are focusing on here. As everyone knows, activity has a dramatic effect on our metabolic rate, capable of raising it by 500% and more. Higher metabolic rate means higher internal heat production. You run, you get hot, and this applies in the Arctic too.

In clothing terms this means that the down jacket which kept you comfortable sitting down at -20°C would fry you if you started walking uphill. Or to put it the other way the lightweight insulation, which was well warm enough as you hauled your sledge at -30°C, could not prevent you shivering almost as soon as you stopped, with worse to follow.

This well-known phenomenon is traditionally dealt with by wearing several different layers of clothing which can be removed or added. But in extremely cold conditions it can be a major chore to keep altering one's clothing, and it is often more practical to have a major part of one's insulation in one layer, either something that is worn all the time like a down suit on Everest or a simple rest-stop down jacket or an overgarment like the Alpha Belay jacket which can be whipped on anywhere anytime. It is therefore useful to have some assessment of what to expect from these main insulating garments.

As with sleeping bags we have tried to keep our figures simple. We can't give you a comprehensive figure (or even set of figures), so we've given you an indicator instead, a single figure we call the TOT, Typical Operating Temperature.

The TOT figure for clothing means that the item is suitable for people heading into situations where these are the minimum temperatures likely to be encountered, for use from short static periods up to medium/low activity.

It is almost irresistible to go on qualifying this statement:

• The gear would be far too warm for its quoted TOT in periods of sustained high effort e.g.sledge-hauling (at altitude effort is great, but movement tends to be slow)
• It would be OK, but chilly to bivouac in it at these temperatures
• The figures assume you can keep the insulation dry
• High altitude and extreme weather introduce new sets of rules
• Etc. etc. etc.

But allowing for these additional factors in the effort to get it exactly right is literally a never-ending process, and one can quickly get lost in a spiral of statistics, which are irrelevant in approaching an ordinary trip and inadequate for a serious one. For a big venture you will have all sorts of judgements to make and your insulating garments will be just part of your whole clothing and gear assembly.

Conclusion

We realise the rough & ready nature of the TOT. It is based as much on experience as on figures, but as a stand-alone indicator it is still only half-way useful: there are simply too many variables to take it further. Its chief value is to give a broad picture of what you're looking at and to allow ready comparisons between different PHD items.

It was not the intention if the tone of this section on ratings appears to be negative. We certainly believe in informed choice and in buying the best gear (please). But it is just an attempt to warn against the too literal acceptance of any temperature ratings, not just PHD's. They are fine, as has hopefully been explained above, as rough signposts and they are certainly useful to narrow down a general choice.

But the more critical the decision, the more weight you should give to human knowledge and judgement, which can bring into play the relevant variables. As always experience, your own and other people's, provides the best and subtlest guide.