Hiking clothing is made up of three different layers. This is the general rule for creating a versatile, comfortable hiking outfit that can be altered during the hike in order to correctly accommodate you and make you much more comfortable while you are on the move. One very important part of this system is the third and final layer of clothing that you need; the outer shell. The importance of this layer is easy to deduce; it is the only layer that is in constant direct contact with the outside world. It can also help in other ways such as provide a way to help the body rid itself of moisture and also providing a good amount of protection from chafing, cuts, scrapes, and any other type of damage that would be sustained without it. Heli boarding 

The theory behind Outer Shell materials is the fact that a water drop is much larger in size than a water vapor molecule. In essence, combining waterproofness with breathability boils down to finding a membrane with a pore size much smaller than a water drop but much bigger than a water vapor molecule. In 1976, Gore-Tex was developed which is a membrane of a petrochemical polymer called polytetrafluorethylene (PTFE). Since 1976, many variations of Gore-Tex have been developed which fall under the category name of PTFE laminates. Heli ski

Keeping outside moisture out is probably the most important task and, unlike breathability, waterproofness depends on more than just the fabric. Here are some guidelines on judging waterproofness:

•     The most important factor remains the fabric. As explained in our section on Tent Characteristics, the waterproofness of a fabric is measured in pounds per square inch (psi) of water pressure. Standard ISO 811 signifies the testing of the waterproofness of fabrics under their actual usage conditions. For an outdoor clothing Outer Shell, a score of 40 psi would signify a good state of waterproofness.
•     Seams - Just like in Outdoor Tents, seams are the vulnerable spots in Outer Shells. Seams should be sealed and coated well to prevent leaking. If possible, look for as little seams as possible and avoid seams in vulnerable places such as shoulders and upper back.
•     Zippers - Zippers are another weak point in your defense against moisture. Nowadays, waterproof zippers do exist so ask around. Otherwise, look for zippers that are well-shielded.
  

As long as you use a proper, three layer system which includes a good quality outer shell that can protect you, your hikes should be much more comfortable and enjoyable for you to take part in. The three layer system is pretty versatile and can truly help you adapt to your surroundings much more easily. In most cases, the three layer system is pretty important, however, the third layer is mostly used for the upper body. This is done mostly in order to protect your torso and neck more effectively since they are very important parts of the body. Even so, the three layer system can often be used to protect your entire body whenever you end up in extremely cold weather conditions.