Optimize the effectiveness and versatility of your clothing by wearing it in a system of layers. The basic outdoor clothing system consists of 3 types of layers: a layer next to the skin, insulating layers, and an outer shell layer.

1. Layer next to the skin: should allow perspiration to pass through and evaporate without absorbing the moisture, keeping your skin dry. This wicking process can be vital to keeping you warm, because wet garments in contact with the skin cause 25 times more heat loss than dry ones.
2. Insulating layers: should trap warm air next to the body. The thicker the layer of trapped or "dead" air, the warmer you'll be. You usually stay warmer by wearing several light, loosely fitting layers rather than one thick garment, because the multiple layers trap more layers of air.
3. Shell layer: should provide protection from wind and rain, which can cause heat to be drawn away at an alarming rate.

• Natural fibers:In the early days of backpacking, natural-fiber clothes were worn exclusively. Natural fibers share the characteristic of readily absorbing water. They are becoming obsolete for the same reason.
• Synthetic fibers: Modern, high-tech synthetic fibers have virtually replaced natural fibers in backpacking clothing. Synthetic fibers are generally hydrophobic, which means they tend not to absorb moisture. Garments made of synthetic fibers do absorb some moisture, bit mainly only in the vacant spaces between the fibers rather than inside the individual fibers themselves. When wet, most of the moisture can be wrung out the rest evaporates quickly.

Your shell layer should keep you dry, comfortable and safe by keeping the rain off of your skin - waterproofness - and allowing your perspiration to escape - breathability.

Rain parkas and pants are generally made of nylon, which itself is not waterproof, so rain garments derive their waterproofness from a number of different fabrication methods and treatments applied to the nylon, each with varying levels of breathability. The amount of breathability you need depends on personal body structure, metabolism, your level of exertion while hiking, and your budget. Extra breathability often demands a higher price.

1. Waterproof, but not breathable: The simplest method is to cover the nylon garment with a waterproof, nonbreathable coating, such as polyurethane. Polyurethane coatings are lightweight and relatively inexpensive, but they are not very resistant to abrasion or mildew. Although polyurethane keeps rain out, it also seals in sweat and water vapor. If you're working hard, the sweat you generate doesn't have a way to escape through your shell layer, and you won't stay dry.
2. Much better breathability: Waterproof/breathable coatings were designed to attack this problem. These coatings, applied to the inside of the nylon shell, have billions of microscopic pores per square inch. The holes in the waterproof/breathable coating are large enough to let vapor escape but too small for raindrops to get in, so the coating breathes while staying waterproof. As you might expect, high-tech coatings like these are more expensive than polyurethane. Like much backpacking equipment, waterproof/breathable coatings go by a variety of brand names.
3. Even better: A laminated waterproof/breathable membrane, instead of a coating, is also perforated with microscopic pores. Membranes work on the same theory as coatings but are instead fabricated as a separate layer inside the nylon shell. Of these membranes, Gore-Tex is the best known. Gore-Tex garments are typically even more expensive than those with waterproof/breathable coatings, but they have a longer functional life if they are cared for properly.
4. Nothing's perfect: Although the waterproof/breathables are a marked improvement over old-style coated nylons, if you work hard, you will exceed the garment's ability to blow off steam, and sweat will condense inside the shell. Once in liquid form, the sweat can no longer escape through the garment, and you're back to the original problem. Thus it is important to go for the right amount of breathability.