It seems logical that in a rainstorm, if you cover yourself in any material that’s 100% waterproof, you’ll stay dry. Unfortunately however, this isn’t the case for long.
Similar to the previous discussion on sleeping bags, the body has a requirement to give off moisture. Exertion on the part of the wearer compounds this problem. Any fabric that will keep water out, will keep moisture in.
When it comes to waterproofness, the key lies in the ability to release moisture. In a personal rain protection system, most tend to be ‘closed,’ with limited breathability.
In 1969, Bob Gore discovered a versatile new polymer that had spaces small enough to stop water in liquid form. but large enough to allow water vapor to be released through the fabric. This allowed rainwear to be waterproof and at the same time breathable.
Since this time, many similar products have been introduced to compete with Gore=tex. Although this has aided people greatly, it hasn’t fully addressed the problem.
Although it’s in many ways a miracle fabric (that has been integrated into all types of clothing and into shoes), the fabric is only breathable enough to exhaust approximately one-third of the moisture produced. This is however a big step toward people remaining dry.
If you decide to purchase a piece of Gore-Tex (or similar) clothing, many manufacturer will also include breathing pockets. These appear to be like regular pockets, but they simply open the fabric to the inside of the material. This provides for further breathability.
Like we discussed with sleeping bags, many types of insulation material will lose loft when they start to absorb moisture. This results in heat loss. This is especially critical in cold conditions. Every effort should be made to remain dry.
Remember not to exert yourself too much and remove layers as required. Staying warm and dry is key to long-term survival.