Layers are designed to keep you comfortable and protected no matter what the weather is. Whether you are traveling though a cold wet terrain or a hot dry terrain you should pack and wear layers to protect you from the elements. Material technology for hiking and backpacking is a fast evolving area with many brands competing to get you wearing their brands. This is good for you as a consumer because it now means you can get fairly cost effective clothing that will protect you in most situations you will come across. Although these may still be a little more expensive than some clothes this is an investment that will ensure many happy hiking experiences. There are three layers that are crucial to backpacking; the inner, the middle and outer layer.
INNER LAYER
This is the layer that rests against your body and for that reason should have the most time spent on it. As this layer will be resting across your skin you should make sure that you test the fabric for allergies, most good outdoor shops will have display pieces that you can feel. The best technology is worthless if it's not comfortable for you to wear. Bottom layer fabrics should be able to hold warmth in whilst remove moisture away from your body. Fabric choices include polypropylene, polyester, merino, silk and countless numbers of brand names. The staff at your outdoor specialists should be able to recommend the fabric best suited to your hiking needs. Thickness should be determined by the environment you are traveling though, though choosing a fairly light layer may be best as warmth can be accounted for with the middle and outer layer. Even in hot environments a fabric which covers your legs and arms is best as it shields you from the sun, adds protection against biting insects and protects you from the various fauna that likes to shred skin off your body.
MIDDLE LAYER
In cooler environments this is the layer which will keep you warm. In warmer environments this layer may be light or non-existent. This layer is the more casual layer of the three and should be made to fit the environment. For cooler places fleece is a really good option for warmer places this layer may consist of shorts and a tee-shirt as more of a modesty thing to cover you inner layer.
OUTER LAYER
This is the most important layer for protecting yourself from the elements. Good wind and waterproof jackets are usually quite expensive but next to footwear is one of the best investments you can make in hiking gear. Even areas of drought can have sudden downpours and thus you should never be without it. A good jacket will be able to protect you from all the elements but at the same time be comparatively light, and easy to put on or take off. You should test the water proof ability of your jacket regularly as this can fade with time, if your jacket does have leaks these are often cheep and quick to repair, and much worth the time verses not doing it. There are a couple easy tests to check how water proof your jacket is, one is by getting a friend to dump a bucket of water over you, or another is to stand in the shower with your jacket on. No matter what the weather gaiters are a blessing as an outer layer. These are basically a pipe of material that fits on your lower leg and covers the top of your shoes/boots. These stop water from entering your boots as well as keeping small stones and plant parts out.
Preparing good layers may take some time the first time around, but once you have invested in these it will be fairly easy from then on. Always prepare your clothing based on your environment and always be prepared for sudden changes in the weather. It is the sudden changes that catch people of guard that cause the most problems in the outdoors, by being prepared you can avoid unnecessary injury or even death.
Advice in this article is written mostly from personal experience but is also built using information from http://www.golite.com/howto/backpackingdetail.aspx?d =180
Outdoors shops are invaluable sources of information and great ways to find out about the local conditions, even if you are not planning on making a purchase stop in to ask for information, they are usually happy to help.