Keela, a Scottish outdoor company, claims a significant innovation in waterproof breathable technology, “System Dual Protection” (SDP). While this technology is much heavier than current 2.5 layer PTFE and Polyurethane based WP/B fabrics, Keela claims it will keep the wearer drier than current WP/B fabrics by reducing condensation on the inner surface of rainwear.
Keela believes the real test of a rain jacket is how dry it stays on the inside. They claim their new technology reduces condensation on the inner surface of their rain gear significantly compared to other WP/B fabrics. To prove this they’ve done extensive testing of rainwear in cold, rainy environments. They also developed an apparatus to simulate these conditions and test the performance of WP/B fabrics. Keela claims that their SDP measurably outperforms current WP/B fabrics in cold and rainy conditions when worn for an extended period of time with an exercising user.
The Keela Cumulus at 24 oz is currently the lightest rendition of the System Dual Protection technology. Lighter fabrics might bring SDP garments into the 12 to 16 oz range.
Keela claims that current moisture transport tests of WP/B fabrics do not simulate real world cold and rainy conditions – the conditions one is most likely to encounter when wearing a rain jacket. That is, a warm humid environment inside the jacket created by an exercising hiker and a cold damp and rainy environment outside. Under these conditions, the inside of a rain jacket condenses in the same way your car windshield fogs up on a cold damp day. The warm moist air from your body hits the cold inside surface of the rain jacket (chilled by contact with cold rain and the outside air) and condenses into liquid water.
Keela apparatus to test garments in “real world conditions” – cool, wet and rainy. Standard PTFE and PU laminates come up with a wet inner surface. Keela System Dual Protection garments have a much drier inner surface.
Since the outside of the shell is just as wet as the inside there is no force to move water from the wet inside of the jacket to the wet outside of the jacket. That is, there needs to be a moisture differential (wetter inside and drier outside) to create a motive force to move the condensing water to the outside of the shell. So as long as you exercise in these conditions, water continues to accumulate on the inside of the shell and soak your baselayer and whatever other clothing you have on inside of the shell.
To solve the condensation problem Keela uses an approach similar to a double paned window. They use two hydrophilic WP/B membranes separated by an air gap. This is their “System Dual Protection” (SDP). These are not bonded but are two free hanging fabric layers.
How does it work? First, the air gap between outer and inner fabric layers creates an insulating barrier between the inner and outer surfaces of the rain jacket fabric keeping the inner surface warmer and less prone to condensation. Keela claims that it also keeps the wearer a bit warmer and reduces the number of layers. Note the focus on cold, damp, and horrid conditions as encountered in Keela’s homebase – Scotland.
Second, the inner hydrophilic membrane has a high wicking star yarn polyester liner (which acts similarly to a sponge in absorbing the moisture). Inner moisture is absorbed through the jacket lining and passed though the inner hydrophilic membrane to the air gap between fabric layers. Once here, it cannot wick back through the inner hydrophilic membrane liner as the waterproof laminate will not allow it. The moisture in the air gap between the two fabrics escapes through the outer fabric at its own rate, or it can literally drain down between the two fabric layers and exit via the bottom hem of the jacket. A bellows effect between the two fabric layers as you move also helps to transport water from the inner layer.
What’s the catch? Well for one thing, the lightest rendition of this technology uses two layers of 70 g/m2 fabric. That equates to a jacket (albeit sturdily built and with lots of features) that weighs 20 to 24 oz. Also in warm environments the added insulation of the dual layers may keep you hotter than you want.
For the US market, we could see a jacket with two 30 g/m2 fabric layers coming in between 12 and 16 oz. If the technology is as good as Keela claims, its performance may be worth the weight for hiking in climates like the Pacific Northwest and Scotland.