The Columbia OutDry EX Featherweight Shell has recently come to our attention through a detailed comparison with other waterproof breathable (WB) jackets. This jacket is special in two ways: it has a very high moisture vapor transmission rate (MVTR) and it has no face fabric. The MVTR is important (and the author compares it to three other jackets), as it is a measure of the rate at which water vapor passes through a material (also referred to as breathability). The lack of face fabric allows the fabric to never “wet out” (this is when the face fabric is saturated with water). This will eventually happen with any of the various treatments used on face fabrics and greatly reduces the MVTR. The reason this decreases MVTR is that when the face fabric is saturated with water, it acts like it is 100% relative humidity (% RH) on the outside. In order for water vapor to pass from the inside of the jacket to the outside, the % RH has to be lower on the outside than inside. This is also the reason why if you are generating a lot of sweat and heat and it is humid out, you will feel like you are getting wet from the inside (the moisture can’t efficiently transfer from the more humid interior of the jacket to the exterior). The author maintains that while no current WB jackets breathe enough to be comfortable under exertion (like when backpacking), this is the best yet.
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