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DriDown Bags Debut at REI; Sierra Designs Lab Director Explains Water-Repellent Down

Science, it appears, has hatched a way to make goose down, the most prized insulator in outdoor gear, resistant to its greatest nemesis—moisture.

Men's Zissou +15Sierra Designs is the first gear-maker to bring water-resistant down in sleeping bags to market. Its first collection arrives in June: 3 men's Zissou bags, rated 6°F (3 lbs. 1 oz., regular length, as are the other men's weights shown here), 18°F (2 lbs. 11 oz.) and 27°F (2 lbs. 1 oz.), and 2 women's Eleanor bags, rated 19°F (3 lbs.) and 29°F (2 lbs. 9 oz.). The temperature ratings shown are European Norm (EN) Limit Ratings (for men's bags) and EN Comfort Ratings (for women's).

If you're an early adopter, advance orders for the bags can be placed at REI.com right now. REI is the exclusive retailer for the rollout of these bags and their eyebrow-raising technology, which Sierra Designs calls DriDown. Jackets equipped with DriDown will be released in the fall.

Key claims by Sierra Designs about DriDown:

• Stays dry 7 times longer than untreated down (based on a bulk water absorption test method developed by Sierra Designs).
• In humid and wet conditions, retains 34% more loft compared to untreated down.
• Dries 33% faster than untreated down.

Is water-resistant down a potential game-changer in outdoor gear? Dr. Frank Kvietok, Director of Sierra Designs' Advanced Development Center in Boulder, Colo., that developed the technology, thinks it can be.

"It's been one of the holy grails pursued within the outdoor industry for a long time," says Kvietok, who spent a decade at Procter & Gamble leading R&D projects before switching to the outdoor industry. "Folks have been working on it off and on for years. Once I started digging into this, I was actually sort of surprised we hadn't tackled this challenge earlier and more aggressively. It's totally doable."

SD women's Eleanor +30Why DriDown claims turn heads: Water is to goose down what kryptonite is to Superman—a defense-piercing element that cripples the hero, strips away its strengths and renders it useless.

When plump and fluffy, goose down is very effective at capturing body warmth even though it is incredibly light. When saturated, though, down goes flat. A wet down bag is nothing but a soggy, heavy lump of ineffectiveness.

So despite down's many virtues—lightweight, exceptionally warm, easy to compress, durable and soft—shoppers have been apprehensive about choosing down products for outdoor use.

"You hear all the warnings: 'Don't let down get wet.' It's right there with 'Cotton kills!' " Kvietok says. "It's to the point where so many folks don't even give down a chance."

Sierra Designs is not alone in its quest to develop water-resistant down. A competing technology, DownTek, will appear in a line of outdoor apparel later this year, and other manufacturers are likely to pursue their own take on water-repellent down.

Skeptical? That's understandable. Kvietok, a product of the University of Colorado's graduate school for chemistry, spent 40 minutes on the phone addressing questions about a technology that initially sounds too good to be true.

REI: Should I call you Dr. Kvietok?

FK: Only my mother-in-law insists on that.

REI: Sierra Designs describes DriDown as a "molecular-level polymer." Is it correct to call it a coating?

FK: We're really only putting on as much as is needed to impart the water-repellent properties. If you go further, you're adding too much weight. You'll begin to compromise the fine, delicate structure of the down, and you're not changing the water repellency of the material. As a chemist, when I hear "coating," it sounds fairly crude. We're using a class of molecules that are very similar to the materials used in DWRs (durable water repellants, applied to the exterior surfaces of rainwear).

Frank KvietokREI: How is it applied? As a spray? How does it adhere to the down?

FK: Water-repellent technologies can be applied in a variety of ways. Immersion in a water solution or spray via atomizers are typical delivery modes, though other approaches can make sense.  We've looked at a variety and continue to refine the system to be even more effective.

REI: What is in the solution, the polymer, being applied to the down?

FK: It's a liquid formulation that is a combination of several different chemicals. When it's in the water, the materials are dissolved into the water and are behaving like individual molecules, and then those individual molecules deposit onto the down. Then a heat treatment triggers the polymerization.

REI: Does the polymer add weight to down?

FK: We've tried to weigh it to see the difference and we can't see any.

REI: Down plumes come from the underbody of geese. Mature plumes are 3-dimensional spheres that are fine and delicate. How do they accept this polymer coating without becoming heavier or losing loft?

FK: It's a matter of how much is put on. Certainly if you were putting on, from a weight-percentage standpoint, anything approaching 1% by weight of the down, you start having a mechanical weight issue of the polymer on the down. For the amount we're using, far below 1%, the weight is virtually immeasurable. That really was the step forward we made in the processing: to address a possible negative outcome of putting something on down.

REI: Does the polymer affect breathability?

FK: We've not seen any impact on breathability.

REI: How durable is DriDown? Can it be worn away or will its performance diminish over time?

FK: So far the testing we've done has gone as far as 30 washing cycles in a machine at a warm-water setting with a traditional detergent, which is obviously not what we would recommend for taking care of a down garment. But to make the testing aggressive, we used these conditions. Over the course of the 30 washings we saw no diminution of the original performance.

Is it possible that the treatment can be worn away? Theoretically, yes, it's possible, and I'm sure by the time we get to 1,000 washes we'll see an issue. But within a realistic lifetime of the garment, so far we don't see it.

REI: Have you perceived any negative impact of applying the polymer to the down?

FK: It makes it incrementally more expensive. But from a down property standpoint, no.

REI: Why was 600-fill-power down chosen for the debut of this technology?

FK: We wanted to make sure we would introduce this technology in a product that would be accessible to a majority of consumers. The polymer results in a relatively minor upcharge for the down. It's more about the inherent pricing of an 800-fill sleeping bag versus a 600-fill sleeping bag.

REI: Can the coating be applied to more mature down such as 800-fill with the same results?

FK: Absolutely.

REI: If I tied a DriDown bag to an anchor, dropped it into a lake and left it submerged for 10 minutes, how would the treated down respond?

Promotional comparison photo from Sierra DesignsFK: A lot of the bulk-water interactions, of course, are first determined by the shell material and how the shell material deals with bulk water. The more challenging and insidious form of water is when it's in vapor phase, whether it's humidity or sweat. Shell materials are more designed to pass that water through.

With respect to that dunking in the lake situation, the down will probably be OK for a couple of minutes, but that's largely a function of the shell material.

REI: What would be your time estimate for drying it out?

FK: Wetting out (becoming fully saturated) takes 7 times longer than untreated. The drying time (back to original condition) is 33% faster than untreated.

The quantification we've done is based on methods that we had to develop. When we started this work we pretty quickly realized that the down industry and the outdoor industry had not established any method that really asked the question, "How does down do in the presence of water?" Not just relative humidity, but what happens when it's really exposed to bulk, liquid water?

We are working at converting those methods into industry standards, and we're working with numerous outside labs to assist in doing that. Compared to untreated down, treated down resists wetting out—meaning becoming saturated with water—7 times longer.

REI: My estimate for a soaked down bag to dry out is around 48 hours. But soaked bags are rare. How about ridding a bag of the moisture that may accumulate from our own body vapor?

FK: Humans typically expel a half-liter of perspiration during a night of sleep. Any down bag will absorb moisture over the course of a night. Ideally, you allow for some drying time in the morning before stuff sacking. With DriDown, you get an hour's worth of drying in 40 minutes, about 33% faster.

REI: Are these figures calculated with any external boost to the drying process, such as a fan?

FK: For drying, we use static, ambient room temperature.

REI: How would you assess DriDown's in-the-field performance?

FK: We did lots of field testing and iterating on the lab methods to ensure that they replicate what's really happening.  For instance, when down is exposed to water it's usually a dynamic, moving situation. Whether you're wearing a jacket or using a sleeping bag, you're pushing and pulling against the down's loft. Assessing the down's water resistance has to take into account these compressive and mixing forces.

REI: In frigid conditions, how does DriDown cope with condensation that body heat can potentially create inside a sleeping bag?

FK: Inside a bag, where you are, is the hottest portion of the system. As you move away from your body, temperatures are going down until you get to the shell material of the sleeping bag. At that point, if that temperature at that surface is above the dew point, the moisture will be able to evaporate. If it's not, then the moisture will not be able to leave. It's trapped.

Because DriDown's loft is maintained more so than untreated down, the bag will stay considerably warmer. In our own internal testing using an environmental chamber to control conditions, we've seen as much as a 30% loss of loft for an untreated down sleeping bag compared to a DriDown sleeping bag over the course of an 8-hour period. For down, loft directly translates to warmth. These findings compare well with those of the more controlled methods we ultimately had conducted by an outside lab.

REI: How much field testing was done for DriDown bags?

FK: We've done extensive field testing, lots of different environments and weather conditions. All the findings and observations are consistent with the trends from the lab work. The hardest part is getting folks to use the untreated, control version of the product.

REI: Have you tried out the bags?

FK: I have. For instance, my son and I camped under a tarp during a backpacking trip in the Indian Peaks last September. It rained and hailed and snowed. My son had the DriDown bag. The tarp held up well. We were both dry and comfortable in the mornings.

REI: Does DriDown contain any chemicals that could pose a health risk?

FK: The technology at the chemistry level and technology at the application level are both Bluesign-approved. (Bluesign is a textile industry standard that considers the issues or environmental, health, safety and resource conservation.)

REI: Can you think of any negatives associated with this polymer?

FK: We've been looking for them, trust me. When we first got ahold of this and started looking into it, we thought, "Wait a minute; we have to be missing something." We have looked, and this looks solid. The only negative we can think of is the little incremental cost.

REI: How long have you guys been working on this?

FK: Off and on for years. We really put the pedal to the metal about a year and 3 months ago. You just have to roll up your sleeves and do a bunch of experiments and figure out what works.

Photos, top to bottom: Sierra Designs men's Zissou 18°F; women's Eleanor 29°F; Frank Kvietok in the Colorado backcountry; a promotional photo from Sierra Designs that shows DriDown afloat atop a beaker of water; a side-by-side view (below) of untreated down and DriDown photographed at REI.

Posted on at 12:59 PM

Tagged: DriDown, Sierra Designs, down, goose down and sleeping bags

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