Insulation is a very important component of layering. Its main functions are to keep body warmth in, cold air out, and to wick away chilling moisture to the outer layers, where it can evaporate. The materials you’ll usually find when looking at insulation are down, fleece and synthetic materials.
Pros – Down is about as flexible and convenient a material as you can find. It is a fantastic insulator. And for the amount of warmth it provides, it is extremely light. It also compresses into a surprisingly small size, making it an ideal insulation choice, when space is at a premium.
Cons– Down is a very sensitive material.When down loses its “fluff”, it loses its ability to trap dead air and subsequently doesn’t insulate nearly as well. Down also must remain dry to retain its insulative properties. If it gets wet, it loses a substantial amount of its insulating ability. Because of this, down can only really be used in dry conditions, or as insulation in a jacket with a waterproof/breathable shell.
Pricing for down can vary quite a bit. The bigger the down feathers, the bigger the price tag. Bigger down feathers can stand up to more of a beating and don’t lose “fluff” as quickly, after repeatedly compressing it. This is important because insulation traps still air between your body and the outside, which your body then warms.
Down Fill Power
The quality of down is often expressed as the fill power of down. Fill power is the most frequently used measure of down quality. It involves measurements taken of a one ounce sample of down in a plexiglas cylinder with a weighted piston compressing the down. A parka (duvet or sleeping bag) made with high fill power is lighter and more compressible than an equally warm one made with lower quality down. Fill power is expressed as cubic inches per ounce (in³/oz). A lofting power of 400–450 is considered medium quality, 500-550 is considered good, 550–750 is considered very good, and 750+ is considered excellent.
Pros – Fleece outerwear is great for rigorous outdoor activities as it dries quickly and can be layered under a shell for wind and rain protection. Additionally, fleece is lightweight, and just feels good to wear.
Cons – Fleece is not windproof or waterproof. Wind and water will penetrate the fleece reducing its warmth and dryness. Also fleece can be pretty bulky and might take up a lot of room in your pack.
Wind Stopping Fleece
Most fleece will allow wind to penetrate the garment and will not keep you as warm in windy conditions. Due to this liability, some fleece has been constructed with a wind barrier integrated into the garment to prevent wind from penetrating.
Synthetics are not as compressible as down, but perform well, wet or dry. They can dry reasonably quickly, are wind resistant, and are usually less expensive than down. Synthetic materials are a good decision, particularly if you are facing the real possibility of getting wet.
Choosing What to Wear
There are appropriate times to wear down, synthetic, and fleece clothing. These tips will help you decide when it is a good time for each.
Be prepared for weather
If there is a chance of precipitation, or even if there isn’t, be prepared to deal with it. Getting wet in the winter is much more serious than getting wet in the summer. Before you venture out, you have to spend some time thinking about how you are going to stay warm and dry. These should be two of your top priorities.
Know how hot you’ll get
If you’re planning a peak bagging trip, a fleece and maybe a synthetic jacket for very cool weather would be good. For activities like alpine skiing in dry weather, wind stopper fleece, interchange parka or shoftshell jacket would do well. Also, remember that women, thinner people, older people, and people with slow metabolisms will get cold more easily than say a bulkier guy, so dress accordingly.
Layering is only effective when you do it properly. Yes, keeping on your layers will keep you warm and toasty, but when you start heating up you should stop and take a layer off. You always want to stay as comfortable as possible. Try to keep yourself from sweating by removing layers as needed, and if you start getting cold again put a layer back on.