In the breathability test, also called the "sweating hot plate," a fabric sample is placed over a warm testing device that emits water through small pores. The speed at which moisture vapor moves through the fabric determines its breathability (that's how Gore calculated the 25 percent margin you mention for XCR). The Suter test measures the fabric's ability to keep water out under pressure by placing it beneath a glass column filled with water. The taller the water column, the greater the pressure. In wind tests, of course, the fabric is simply tested for its ability to block wind.
However, I'm unaware of an independently commissioned study of all the main fabrics out there. The results are almost always published by one gear maker or another. And then you get into disputes about whether the test reflects real-world conditions; for example, what happens if the fabric surface is wet, that sort of thing? My own feeling is that people are insisting on paying less for rainwear because of the lack of clarity on this issue and the reality that most waterproof-breathable fabrics actually under perform in many conditions. I haven't seen any gear makers launch any new $450 jackets for a few years now. Furthermore, lots of sub-$200 products now dominate the market.
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