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Old 12-07-05, 02:31 PM
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Gojohnnygo.
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I just wanted post this.


How Gore-Tex® Works

The human body is a heat engine, and the heat your body produces drives the breathing of Gore-Tex. Without a temperature differential of warm on the inside and cooler on the outside, most waterproof/breathable rainwear barrier systems will not function properly. Your body gives off heat and sweat all the time, more of both when you are working harder. The water in sweat has to become a vapor in order to get through the Gore-Tex layer because water droplets are too large to fit through the PTFE film pores. This will happen on it's own, but without the heat differential, vapor passes both ways in equal amounts.

The body heat generated evaporates the sweat off the skin, which condenses again when it cools enough (it hits a cool surface). It also condenses when it reaches a concentration at which it cannot stay a vapor. Normally, the heat buildup under the Gore-Tex layer is enough to keep most water in vapor form and in continuous migration away from the heat source (your skin). But, when vapor transmission through the barrier film is inhibited for some reason (see the next paragraph), condensate builds up inside and slowly wets the clothing layers next to the skin.
Gore-Tex Will Sometimes Seem to Quit Working

Gore-Tex is good stuff, but not fool-proof or fail-safe, and nothing lasts forever. One big factor in Gore-Tex's waterproofing is what Gore calls "Durable Water Repellency" (DWR). This is a water repelling (hydrophobic) chemical coating applied to the outer fabric of the Gore-Tex laminate that causes water landing on it to bead up on the surface of that outer layer, and roll down off the garment. If rain water or wind blown wet snow from pedaling is not shed relatively quickly, it will soak the outer fabric, which impedes vapor transmission through it, greatly inhibiting the breathability of the Gore-Tex barrier film just underneath.

There are no permanent water repellent compounds yet available, so what is being used must be reactivated or renewed periodically. When it does fail, the effect appears to be a leak -- as if water is passing from the outside through the waterproof layer to the inside, and soaking the clothing underneath. That is not the case. The human body produces more water than most people believe. The water inside the Gore-Tex is almost always vapor unable to get through the saturated fabric layer outside the barrier film which has condensed on the inside surface and feels like leakage. You can tell early-on when this might be happening by water on the outside starting to wet areas on the outer fabric layer of a Gore-Tex garment. This condition does not defeat the waterproofness of the fabric, but does inhibit its breathability significantly. It often, but not always, starts in areas of high abrasion, and where water can collect, like the front of your arms,lower legs, and backside. When the DWR fails and vapor transmission is inhibited by the wet fabric outside the Gore-Tex layer, condensate builds up inside and slowly soaks the clothing layers next to the skin.

Gor-Tex is not perfect, and even a very new and clean garment with a working DWR can still be overwhelmed by heavy activity. Extra ventilation (like armpit zippers, uncovered openings, etc.) will help, but still may not keep some areas of clothing inside the Gore-Tex shell from getting damp. In extreme cases even downright wet. During rest stops, your body heat will continue to dry your clothing through the Gore-Tex.

If anybody has anything to add please do.

Johnny
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