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For many years the outdoor industry has relied upon the Water Vapor Resistance or RET (Resistance of Evaporation of a Textile) test to measure the “breathability” of water resistant/waterproof fabrics. This test,”compare(s) the ability of different materials to dissipate moisture vapor from the body of the wearer to the outside.” (WSA Jan/Feb2010)

However, in our opinion, the RET test (ASTM F1868 -09) does not accurately evaluative the true breathability of a fabric. In fact, “studies have confirmed that the test is predominantly influenced by the fabric thickness, rather than the pore characteristics of the fabric.” For example, the RET test yields a result that says a three layer hard shell/waterproof fabric is more breathable than a 200 weight fleece. Anyone who has ever worn either of these fabrics knows that’s not true – fleece is almost infinitely breathable (hence the reason Polartec has created other more wind resistant fabrics over the years). In addition, RET tests are affected by clothing weight, drape and tightness. Perhaps most importantly, RET not allow any air movement during the test, so you get some truly bizarre, lab-only results.

Another standard test used by the textile industry to measure breathability is Moisture Vapor Transfer Rate (MVTR). MVTR measures how much moisture vapor can pass through fabric in a 24-hour period and there are over 30 different tests to assess this transfer rate. However, these tests can yield wildly different results (as chronicled in this great post on Patagonia’s blog) and like the RET test, MVTR is static and does not account for real-world conditions where air flow is always present.

As an alternative, Polartec is promoting a better means of evaluating the breathability of water resistant and waterproof fabrics. The Dynamic Moisture Permeation Cell (DMPC) is an ASTM standard test that evaluates a fabric’s ability to move moisture vapor in dynamic conditions. The test can change air pressure and humidity on each side of the fabric and measure how well it truly breathes as conditions change (like the real world). DMPC was developed by Dr. Phillip Gibson, a civilian scientist working with the US Army. Click here to download an interesting story about Dr. Gibson’s testing from the June 2004 issue of Inside Outdoor magazine.

In the chart posted above as you move to the right on the horizontal axis, you can see that Polartec Power Shield Pro (the blue line) breathes more and more as you increase the pressure – this is roughly equivalent to increasing air speed or wind – like going from standing still to walking to a light jog. The harder you work, the harder the fabric works (both convection and diffusion are at work when air is moving). Meanwhile, the orange line represents a full-film softshell fabric – the line is flat meaning breathability does not change. This translates to a damp sweaty user experience as exertion levels increase.

Polartec has always emphasized air permeability. Even tiny, tiny amounts of air flowing through the fabric massively increases a fabric’s ability to move moisture vapor away from your body. Fabrics without airflow require a significant amount of heat and moisture vapor to build up inside the jacket before they start to work. We have all experienced the sweat-box feeling of a fabric that relies only on diffusion to “breathe.”

Fall 2010 a range of jackets will be available in the new ultimate soft shell – Polartec Power Shield Pro. For more on Polartec Power Shield Pro, scroll down to see previous posts on the fabric launch and on Polartec’s partnership with Finetex.