Water vs. DWR
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Ian Schumann
(freeradical) - M

Locale: Central TX
Water vs. DWR on 12/12/2007 10:41:24 MST Print View

Forgive me if I'm saying anything obvious, as I'm from central Texas and since we don't get much interesting weather down here :-D, I haven't much chance to observe how water does/does-not penetrate the DWR on my various shells.

But last night it was coming down, and I had some free time, so in a dorky move that I'm sure a lot of us are vulnerable enough to admit . . . I went outside and stood around in various different technical pieces that I own, taking note of their breathability and water resistance. Usual drill.

Now what I took note of for the first time was that when it was sprinkling, I could stand out for a while in my OR Ion or my Cloudveil Prospector, and water would bead up indefinitely on the surface of these things, hardly ever wetting through. It seemed like no amount of sprinkling would break the DWR.

When I moved under the leaky gutter 20 feet up that drops a heavy stream of water, a proper miniature rainstorm, both of these items wet through immediately. Not within a few minutes or even a few seconds, but immediately. The DWR seemed no match at all (which could be because I've had both of these pieces for a while . . . but maybe we can ignore that for right now?).

So, what I'm wondering is maybe DWR efficacy is based NOT on the AMOUNT of water (since I can run a medium faucet stream over either the Ion or the Prospector and it will continue to run off pretty nicely) but the VELOCITY of it. This makes sense to me initially since everything I know about real waterproofing is based on pressure, and of course a faster moving rain droplet will create more instantaneous pressure on impact, yeah?

If this is true then I should rethink my clothing systems a little bit. I've been influenced a lot by marketing and by the threads and articles that I see here, and had the impression that if it was going to rain for a long TIME on a trip, I should take a little something more than a wind shell. But now I'm not sure this is true, because my (maybe mistaken) impression is that if it's misting or sprinkling for a long time, these lightweight DWRed pieces will work just fine. And the only reason to take a proper waterproof piece is if the rain will be heavy (and of course, sustained enough that I can't dry out the layer with my own body heat).

Commentary?

Ben 2 World
(ben2world) - MLife

Locale: So Cal
The Limitations of DWR on 12/12/2007 10:56:43 MST Print View

As you probably know, DWR is meant to make a garment more rain resistant -- but not rainproof. The technology of making water bead up and roll off -- instead of penetrating though the fabric -- works best when rain is only misty -- and quickly becomes suboptimal in heavy rain or prolonged rain (and esp. both).

True rainproofness comes with an added PU barrier on the underside of a garment. In this case, the DWR on the top side resists water penetration while the PU barrier physically blocks any water that has successfully soaked the fabric from totally coming through.

But a PU barrier will seriously affect breathability. This is why wp/b jackets just can't compare with wind jackets in breathability. The two exceptions are eVENT and MontBell Breeze Dry Tec laminates -- these two have somehow managed to retain 100% waterproofness while dispensing with PU coating entirely -- and they are the most breathable wp/b garments around.

Logan Wealing
(logonwheeler) - F
DWR Rating on 12/12/2007 11:26:19 MST Print View

Ian,

I also believe (correct me if I am wrong) that DWR treatments are rated based on pressure measurements. The better the DWR - the more pressure (from water) it can withstand. Going along with your experiment, the light misty rain does not present much water pressure on the surface of the DWR. However when you encounter a full downpour such as a heavy rain storm or you gutter test, it presents a much greater water pressure - therefore wetting out your garment.

As Benjamin pointed out, DWR is only the 1st layer of defense against the elements and can (and will at certain times) will penetrate the DWR.

Just my 2c

Edited by logonwheeler on 12/12/2007 11:26:57 MST.

Ian Schumann
(freeradical) - M

Locale: Central TX
Re: on 12/12/2007 11:29:00 MST Print View

Good to know about Breeze Dry Tec (much cheaper than eVent if I recall) . . . if I'm ever in line for a real WP/B, that is.

I guess the point of all this is only that I've realized DWR wet-out is not dependent on amount of water or time of exposure, but water pressure. And instantaneous water pressure is higher with faster, bigger rain drops.

Is that right?

Ben 2 World
(ben2world) - MLife

Locale: So Cal
Re: on 12/12/2007 12:31:19 MST Print View

Yup, makes sense to me. Thinking about it, a non-waterproof garment's only protection from rain penetration is the combination of tight weave and chemical repellant (the stuff that makes water bead up and roll of). If rain is pouring, the higher the pressure, the more it will "punch through" the garment. Tight fabric weave is no substitute for a full layer of PU barrier.

Mike W
(skopeo) - F

Locale: British Columbia
Water vs. DWR on 12/12/2007 12:56:58 MST Print View

It's also important to realize that pressure comes from different sources. In camp, when it's raining (heavy or light) I wear my waterproof pants because I like to sit down on wet stuff (logs, grass) and DWR will soak through immediately. Waterproof is mandatory for me and DWR is important as well because the DWR prevents your gear from getting saturated and is therefore quicker to dry out when the rain stops. There's no point in buying a light weight WP/B jacket if you are going to be carrying an extra pound of water around in the jacket after a rain storm.