I think that dressing for the outdoors is a little bit of a lost art in our central heating/air conditioned world. If you want to stay warm then the only thing that provides any real insulation is dead air, air which does not move. As pointed out by many, what you dont want to do is sweat as this can be a problem with chilling when you stop activity. The key then to staying warm in my book is learning to regulate your temperature properly. Though this took some practical experience to achieve, I learnt that dressing in a certain way makes it a lot simpler.
I always aim to be comfortably cool when outdoors and standing still, not cold but almost so. This way, any mild activity around camp, or on-the-flat walking, can be undertaken without any significant overheating.
Being in this cool state also reduces my water consumption considerably, but as has been pointed out already you get dehydrated very quickly in the cold. Apparently the reason for this is that below freezing your lungs actually have to moisturise the air you breathe for the oxygen to pass through the membranes, all that seeing-of-breath is actually precious hydration being lost. The human body also produces stress hormones when cold which increase your urination, we have all been there!
I got severely dehydrated once while canoeing in autumn, I was border line hypothermic when I woke-up in the middle of the night. I managed to get the fire stoked up and with very wobbly club hands make some coffee to repair things, but I did give myself a scare. Anyway you get the point, drink lots.
The trick to clothing is management of the dead air insulation. I have found my shell is, daft as it sounds, the most thermally important bit of clothing. It should be highly breathable and totally wind proof. I dont like Gore-Tex as the so called breathing pores dont work when its cold, to boot your jacket gets to act as if its made of cardboard. (Just my opinion, if you want to walk about in a plastic bag, then who am I to say youre wrong.)
I wear Ventile; this stuff becomes fantastic in cold weather. I have found the key to a good Ventile smock is that it has a permanently attached hood (never underestimate the value of a good hood), large enough for my head and neck insulation, which can be cinched tight around the face. It should also have Velcro closure wrists and an elasticised hem draw cord. All these features, though not high fashion, allow you to regulate air flow through the jacket. A big dump pocket on the front is also useful, more on this later.
If its really cold, over trousers in Ventile are also very useful.
Footwear is a little problematic; you really want two thick pairs of socks, a thermal insole and a leather boot. Unfortunately footwear in the cold is always a compromise. Your boot needs to be loose for your foot to stay warm for two reasons. Firstly any tightness will restrict blood flow to your foot, secondly the movement in the boot while walking will pump air through your socks removing the moisture and keeping them comfortably cool while active and toasty when still. The thermal insole provides a conduction barrier between you and the ground and is in my opinion essential.
The problem with lose footwear is that it can cause blisters and instability on rough terrain, cant have everything I suppose.
I lump base layers and insulation together as there is a lot of marketing boll**ks thrown about on the subject. Its your body heat that drives moisture out of your clothing (so called wicking), if you have too much insulation on, water vapour (sweat) will condense in you clothing regardless of what it is made of. If this is cotton it will absorb a lot of this condensed moisture and when you stop, chill you quickly as body heat is used to dry out the clothing. (Cotton actually wicks as well as any other fibre, most oil lamps are testament to this fact).
Wool is a little better but still absorbs a lot of moisture if you get your temperature regulation wrong. According to people more knowledgeable than me, due to its fibres natural hydrophobic surface properties ( something to do with scales), it stays warmer as it dries progressively through its thickness rather than actual wick backwards like cotton. (Dont tell the marketing men but surface tension wicking actually works both ways, wool works because it inhibits reverse wicking when there is a relatively small amount of temperature difference, manmade fibres work because they absorb such a tiny amount of water, as such both work well as insulation).
With traditional wool insulation in cold conditions, it is necessary to build a fire and dry out the garments or else you end up carrying a few kilos of frost around with you and eventually this ruins the insulation properties of wool and you freeze. (I wear wool because it can be dried fairly forcefully with a fire unlike manmade fibres, this is VERY important if you take a cold dunking in a canoe. Wool must be kept clean as any dirt actually causes the reverse wicking by inhibiting the fibres hydrophobic surface properties)
All this is a very technical monologue and I apologise if Im boring anybody.
There are two items of clothing that I feel are totally underrated the mitten and the scarf.
Mittens are the ideal hand cover for cold weather. I attached mine via a cord through my jacket kiddie style. This way they dont get lost. Mittens are useful as to do any dextrous tasks requires me to take any hand coverings on and off a lot. Gloves are too much hassle, tend to restrict my circulation and I still have to remove them to do even basic tasks. Also I have found the increase surface area of a glove chills my hand significantly if it gets wet, which it always does around water. I use a pertex/pile mitten (buffalo) that dries very quickly and is windproof. It has a good secure Velcro closure, no good by a fire but then I dont need my mittens on by a fire.
For some unknown reason scarfs have gone out of fashion. A good scarf is in fact ideal for the outdoors. It provides insulation to the neck area, which is a major source of heat loss, and provides a seal to stop warm air escaping from the shell. It provides as much insulation when applied to the neck as if wearing another thick body insulation garment, and weighs much less. Its best feature for me however is in regulation of body temperature when on the move. It can be removed / adjusted without having to stop and take my pack off. (This is where the chest dump pocket comes in useful). By its adjustment I can easily regulate insulation and air flow through the rest of my clothing system.
The scarf is also a perfect companion to my woolly hat as it can provide a balaclava effect without me looking like a bank robber.
I have found the humble scarf is also useful in my sleeping bag as it provides a very good neck baffle come face covering in very cold weather. Firstly it stops my breath moisture getting into the bag and secondly any accumulated frost can be quickly dried out of the scarf in the morning by the fire without having to expose my bag to the flames.
The scarf also stops trickles off my brimmed hat running down your neck when its raining. (While not life threatening, this can ruin the moment.:Wow: )
They say to get ahead get a hat. I say to stay warm outside get a scarf.
Finally Id like to share a little trick with you if you are fishing or canoeing. If its cold, first dump your hands in the water and leave them there until they hurt with cold. Take them out and shove them in your jacket until warm again. Now you will have warm hands for the rest of the day without any gloves on. This tricks your circulation system into keeping open the blood vessels in your hands and they dont get cold. If you dont believe me try it, I guarantee you will be amazed.
