In reply to Vivvi:
> I don't know the basic principles of layering - could someone please help?
The essence of layering is balancing the heat generation of your body aganst the heat losses to the environment.
For active sports, body heat is generated largely as a consequence of your muscle activity, and there is a wide variation in heat output between high activity, and rest; factors of 7:1 are not uncommon.
The body controls the loss of excess heat by sweating (and thus heat of vaporisation of the sweated water), so you need a way to allow this evaporated water to escape from your clothing system. Body heat is also lost by radiation, convection and conduction.
When your body heat output becomes lower than the heat losses from body to environment, you need to stop the loss of body heat.
So, a layering system will usually start with a base, or comfort layer next to the skin. Its purpose is to wick sweat from the surface of the skin, and encourage evaporation of sweat. This wicking helps to keep the skin feeling dry and comfortable, and the evaporation aids heat loss.
Next, we will generally add a mid, or insulation layer. The purpose of this is to trap warm air next to the body, whilst allowing the evaporated sweat to escape from the clothing system. If we're not working hard, we need the insulation to keep us warm. If we are working hard, we may need to remove this mid layer, or somehow allow the trapped warm air and evaporated sweat to escape. Thus, mid layers usually consist of material with a fairly open structure, that is efficient at trapping air, and yet allows air moisture to pass through it if necessary. Fleece is very good at this.
Now, in windy conditions, the open, permeable nature of the mid layer means that the warm air can be easily stripped from it, so its insulating properties are severely reduced. One way to overcome this is to use a thicker layer of fleece. However, the downside of this is that it can be too hot when there is no wind, or if you add the next layer.
The next layer is a protection layer or shell, to keep out wind and rain. Traditionally, this is waterproof shell, to keep out rain, since rain conducts heat from the body much, much better than air does, and encourages evaporative losses as well. If a mid layer gets saturated with water, it will no longer insulate, since the trapped air has been replaced by much more thermally conductive water.
Traditionally, the waterproof has also been used as a windproof, to stop the mid layer losing heat. However, despite all the manufacturers claims, their fabrics really aren't breathable enough to allow enough sweat to escape; "Guaranteed to Keep You Dry" should have the caveat "from the outside". You will get wet from sweat on the inside.
A solution to this is to adjust the layering system slightly from a traditional base, 200 weight fleece, waterproof, to add a lightweight windproof layer. This layer is significantly more breathable than a waterproof, and will increase the efficiency of any insulation worn under it, since it will stop warm air being blown out of the insulation. As a result, a lighter mid layer insulation layer can be used; a 100 weight fleece, for instance.
Even then, it can be useful to have good venting options in the outer layer, to control the amount of air that passes through the mid layer, thus allowing you to regulate your temperature.
Now, since you will probably become inactive at some point during the day, since we have reduced the level of fixed insulation in the mid-layer, we may need to add another insulation layer to cope with the reduced heat output of the body at rest. This can be done by adding another mid layer under the shell layer, or by adding an insulating layer over the top of all the other layers. This latter approach is usually called a belay jacket, since it's often worn when your static on a belay... Ideally, this layer will be very weight efficient, using down or a good synthetic down equivalent, so that it's light and compact to carry, but adds a lot of insulation. It might usefully be water resistant, or even waterproof, depending on where and how you intend to use it.
So, we have a five layer system:
base layer
mid layer
windproof layer
waterproof layer
static insulation layer
If it's not raining, your 'action system' will generally consist of some combination of the first three items. When you stop, you add your static layer to reduce heat loss.
With this system, we can cope with a wide range of conditions:
If it's warm and still, you wear a base layer
If it's warm and windy, you wear a base layer and windproof shell on top
If it's cool and still, you wear a base layer and a suitably warm midlayer.
If it's cool and windy, you wear a base layer and a suitably warm midlayer, and a windproof shell to stop the warm air being blown from the midlayer.
If it's raining, you decide whether your windproof will provide adequate water resistance, and, if not, replace it with your waterproof.
If you're static, you can put the belay jacket on over all your other clothes.
Now, there are further complications with the 'soft shell', a very vague term that covers items that span the layer system, depending on the type of soft shell. They can range from things that are base and shell layers combined, to things that combine base, mid and waterproof shell. I find that, whilst they have advantages for specific climatic and activity conditions, they can be a little too narrowly-focussed, and lack versatility. And I have 25 of the things...
If you're new to the layering system, I'd suggest starting with the five-layer system I mentioned above, as it is versatile, and can cope with most conditions. Only when you've got some experience of using it, and knowing what you need, and what seems to work for you, would I suggest that you thinking about getting a soft shell.
Individual layers have advantages over combined layer items:
You can choose the weight of midlayer to suit the weather conditions; lightweight for warmish weather, heavier weight for cooler weather.
You can pick the windproof to suit the activity; lightweight for walking, more robust for scrambling and climbing.
You can replace each of the items as they wear out.
You can wash and proof each layer as appropriate.
On the other hand, individual layers have disadvantages over combined items:
Venting arrangements are harder to combine (i.e. geting vents to line up)
Multiple layers may bind on each other, making movement harder
You can end up faffing with donning and doffing layers all the time.
Hope this helps.