Jul 29, 2013 at 6:58 am #1305957
ok, so I hear this phrase often … rain gear wetting out.
what exactly does this mean ?
does the rain gear become worthless ?
does the fabric simply absorb moisture to the point where its no longer breathable, yet still provide waterproof rain protection ?
even if it no longer breathes, does it provide good wind protection and act as an adaquate vapor barrier ?
does renewing the DWR surface fix the problem ? or do I throw the gear out ?Jul 29, 2013 at 7:13 am #2010504
Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
Wet out is a somewhat temporary condition. Most rain that hits outside will still fall off. Sweat will not be evaporated so you'll get wet from the inside. It will still provide wind protection. It will become clammy and clingy.
After it dries out, it will be more useful again. It can dry out just wearing it if it would just stop raining for a while.
If you put it in drier, iron it, or add DWR treatment you can make it less susceptible to wetting out in the future. Most rain gear will wet out if you're in enough rain long enough.
Sometimes a piece of gear will have to be retired because it's not rain resistant enough.Jul 29, 2013 at 7:44 am #2010510Jul 29, 2013 at 8:29 am #2010520
Cartoon version of the physics: Breathable fabric is basically swiss cheese. The air diffuses through. By using the right fibers in the material, and/or coating those fibers, you can basically make the surfaces repel water in bulk – i.e. rain droplets. In cartoon version imagine big water drops bouncing off the much smaller swiss cheese holes. (yes, all my past physics professors are rolling their eyes, LOL). Now imagine enough of these water drops hitting the swiss cheese that some of them manage to get stuck in the holes. Now the water doesn;t have to squeeze through the holes as a drop. Basically it can just land on the water in the hole (which actually more or less attracts it), merge with that water, and then flow through to the other side. This is the case of "wetting out". Now your fancy rain jacket might as well be a transparent to water. Until you dry out the jacket (and hence the swiss cheese holes) it will not work. However, once you do it will be fine. However this is rather difficult to do in a rain storm, so you are probably SOL until it stops raining and your jacket dries out.
I will add that this picture also help you understand why there tends to be a tradeoff between breathability (size of the "holes") and waterproof-ness, why drying it back out fixes the problem, and why if the coatings wear off over time ("bigger" swiss cheese holes) it will not be as waterproof unless/until you restore the DWR finish. Incidentally in this respect the difference between water repellant jackets intended as windshells (like the Houdini) and waterproof breathable jacket is a matter of degree, not kind. You could wet out even a serious rain jacket (possibly) by holing in under water for a long time.
On the issue of wind protection it is a mixed bag and depends. If the surface of the jacket is separated from you by a layer of air, then probably the wind protection survives to a large degree – convective heat loss will be preserved. Probably a moot point though. Water conducts heat very well, and if the water hits your body, or even other materials next to you body the loos of heat due to conduction may be made much worse, and overpower the wind protection. Once water starts getting inside this is inevitable and things are going to get worse and worse until you can get the jacket dried out.Jul 29, 2013 at 8:45 am #2010529
I appreciate the 3rd grade illustration.
so why do some rain jackets claim to wet out less easily than others ?
how do those pressure numbers fit in to all this ? 10,000, 20,000, 5,000 ?
does this mean smaller holes ?
and how then does the DWR help keep the rain drops from getting stuck in the holes ? to slippery ?Jul 29, 2013 at 9:03 am #2010540
LOL Forget about 3rd grade, I often had to resort to this type of thing with my undergrad pre-med physics students.
Pressure: yes, it can force water through the "holes". Pressure required to do this is one measure of the "size" of those holes. So even though you don't use the jacket under pressurized conditions the number (head pressure) is very relevant for the issue of waterproof-ness
The last question is an astute one. Ultimately it come down to the fact that water is "sticky" (the molecules attract other water molecules). It is a special type of sticky though – it works mostly at an interface boundary, like air/water. If you have ever seen a drop of water on a waxy (hydrophobic) surface it will contract into a little ball. Think of a balloon rather than honey. Then the balloons hit the hole (really, I'm seriously not trying to sound like an idiot here) they will bounce off. They have to overcome the "desire" of the water to stay in balloon form, and the chance they will "pop" and overcome this and get stuck in the holes. It is basically an issue of water in bulk versus water as vapor.
Incidentally the properties of a water vs something else interface are crucial to all life – it determines how proteins fold, and hence how they function, how ions move through membranes and therefore how your neurons work, and so allows your brain to work, and it even keeps all your cells from instantly "exploding"!Jul 29, 2013 at 9:17 am #2010543
so those numbers (5,000, 10,000, 20,000) are, or at least relate to, the hydrostatic head ?
are you saying that DWR coating affects hydrostatic head ? and as the DWR wears off the hydrostatic head of a fabric decreases ?Jul 29, 2013 at 9:41 am #2010552
"does the fabric simply absorb moisture to the point where its no longer breathable, yet still provide waterproof rain protection ?"
"even if it no longer breathes, does it provide good wind protection and act as an adaquate vapor barrier ?"
Yes. The Water Proof breathable feature is provided by a layer of plastic that is bonded to a DWR fabric. When the jacket wets out the DWR coating on the fabric fails and the fabric holds water. No changes occur to the plastic which is still waterproof and windproof. Hower the plastic cannot breath through the water logged fabric until the fabric starts to dry out. If that plastic cannot breath due to the water logged fabric you sweat will condense inside the jacket and you can get wet from your own sweat.
"does renewing the DWR surface fix the problem ? or do I throw the gear out ?" All jackets will wet out if it rains hard enough. However if the DWR wears out the jacket will wet out faster. Reapplying DWR can help restore the original performance. However if the fabric has abraided enough reapplying DWR may not restore the fabric to origninal performance. If that happens its time to get a new jacket.Jul 29, 2013 at 10:18 am #2010566
Justin BakerBPL Member
@justin_bakerLocale: Santa Rosa, CA
The outer fabric is nylon with a dwr coating. (dwr= durable water resistant) In extend rain it can eventually wet out. While water is not supposed to penetrate, the jacket stops breathing.
If hiking in really bad, extended wet weather it doesn't mater much if your jacket is "breathable" or not.
This is just my internet knowledge, I don't have a lot of real experience with extended wet weather.Jul 29, 2013 at 5:49 pm #2010712
Justin, you got it right. A wetted out jacket, while in some pointless cases as I described be said to "block the wind" (that will be the least of you concerns when it happens), a wetted out jacket does NOT breath. It only takes one layer that has all its interstices filled water to prevent any breathing, let alone transfer of water vapor. It could be looked on as a kind of "vapor barrier" in such a case, but likewise most likely the least of you concerns when it happens.
Wetting out will not cause a change in the DWR, but it might be a indication, depending on the garment,that it needs to be refreshed. A Houdini wetting out for example is working as intended – it is supposed to be a very breathable fabric, not a very repellant fabric. So you shouldn't do anything to the jacket if it wets out. If it is a precip jacket then you really need to do it. As pointed out if there is actual damage to the outside (delaminations or abrasions that get through the outer layer) then you choices are more limited.Jul 29, 2013 at 6:26 pm #2010719
Dan DurstonBPL Member
I disagree with the swiss cheese analogy, but I could be wrong.
All WP/B jackets use nylon as the outer fabric with the membrane slapped to the inside. These membranes can ONLY pass water as a vapor (not as a liquid) at any sort of normally encountered pressure (unless they're deteriorating or a poor product like Pertex Shield). The idea of forcing liquid water thru small holes in PU or PTFE is commonly repeated but incorrect statement (unless I'm wrong).
So a non-degraded shell can only pass water as a vapour, not as liquid. The whole appeal of these jackets is that they can sorta breathe (pass water vapour) in the rain – otherwise you may as well wear plastic. Like many other things (ie. heat), humidity is always trying to even out, so if it's 80% humidity in the jacket and 40% outside then moisture will naturally flow out until it achieves an equilibrium. Vice versa can readily happen as well, except that body heat helps push moisture out (ie. a non 50/50 equilibrium), so normally you can always achieve some level of breathing.
"Wetting out" is simply when the water repellant coating on the outside of the nylon fails and water soaks into the nylon. Many people see wet nylon and declare their coat to be "failing" and "not waterproof" when really the membrane could be keeping all of the water out. These water repellant coatings ("DWRs") on the nylon do wear, and eventually they all wear out and need to be restored if you want their function.
When a jacket "wets out" there is a ton of liquid moisture right outside the membrane, which means there is no air with any capacity to accept moisture vapour from inside the coat. So essentially the jacket can't breathe, but normally it's still waterproof. The jacket is just no longer functioning any better than a plastic jacket, and in sustained conditions you get damp from body generated moisture.
Thankfully a jacket doesn't normally wet out everyone all at once (high wear areas go first) so you can usually treat the jacket before things deteriorate too much. There's lots of spray on and wash in treatments to restore a DWR. Normally the ones that require putting the jacket in a dryer work best, but they're also harder on the planet.
Some membranes are barely waterproof so they easily degrade over time and cease to be waterproof (ie. Pertex Shield). In these cases the DWR is the only thing keeping rain out, so when it wets out then the rain comes right through to you. This isn't normal though and it's not really an example of liquid being pushed through swiss cheese. Rather the solid cheese is simply falling apart like feta and leaking en mass.
I've got an eVent jacket where the inner lining has worn off in a lot of areas and the membrane has becomes worn down, so now when the jacket wets out I get wet immediately. In the first couple years the membrane was fine, so wetting out didn't mean a wet hiker. This is why a good inner protective layer for the membrane is important. A lot of the UL jackets with simply rubber printed patterns on the inside don't hold up that well if you use them a lot. That's why I prefer a 3-layer jacket, which has a full layer of material protecting the inside of the membrane (ie. Mountain Hardware Quasar/Blazar).Jul 29, 2013 at 7:26 pm #2010733
@fluffinreach-comLocale: no. california
so : if you wax your car , and then spray water on it, the water beads up. most of the car is actually dry (percentage wise)
once the wax dies over time, water covers 100% of your car in a sheet.
now your car is "wetted out"
what they are trying to tell you is that is 99% of your garment is not got beads of water on it (effectively somewhat dry), there is a chance it might breath some.
if 100% of your garment is sheeted with water, the chances of it evaporating any moisture from the inside are about nill.
the sad truth seems to be that ALL dwr dies over time, and that time in the bush is not a hell of a long time.Jul 29, 2013 at 7:33 pm #2010735
I think your physics are wrong. The DWR doesn't change the waterproofness (and my English is clearly wrong) of the membrane.Jul 29, 2013 at 7:35 pm #2010736
Justin BakerBPL Member
@justin_bakerLocale: Santa Rosa, CA
I don't even bother with wp/b jackets. I just use inexpensive non breathable ones.Jul 29, 2013 at 8:09 pm #2010750
eric chanBPL Member
if you are out long enough in the continuous rain …. especially in high abrasion activities … you WILL get damp at the very least if not wet
plan for it and deal with it …
;)Jul 30, 2013 at 12:26 am #2010800
"I disagree with the swiss cheese analogy, but I could be wrong."
Yeah I know. It was supposed to be a cartoony analogy to help explain why vapor can pass through and droplets could not. And yes, the reason why the water manages to eventually get through is the weakening of the barrier. Whatever the reason, a point on the jacket where the water gets through in a more or less continuous column will actively wick water through. Its not just that there is a "hole", but once there is enough liquid in the "hole" the internal environment of the water is a very low energy path for passing through the membrane. Much lower that a single microscopic droplet will experience. That is what I would call wetting out. That would almost always occur on real rain jacket at isolated points.
The full blown wetting out could only happen in material where the wicking spots could spread – for example as the inner side of the jacket gets wet, especially if it get help along by touching skin or clothes, and then leads to a spread of the wicking area.
I'm not %100 sure how relevant it is modern breathable jackets, but the main point I was trying to make is that the potential for passing more water through the membrane should be dramatically altered by any layers of water on either side. The energy barrier that responsible for the resistance is largely that of the surface energy of the droplets. Remove that and you can can change the properties of the water repellance. To take an extreme example, if you put the membrane entirely under water then water could be expected to pass through the membrane much easier. Another example is if the right kind of contamination gets on the jacket that can act as a surfactant to the water it can lower the surface energy of the droplet and have the same effect. There are a lot of examples of similar things in nature, especially in biology.
Anyway sorry for nerding out.Jul 30, 2013 at 6:34 am #2010837
Greg MihalikBPL Member
I'm pretty sure GoreTex passes only vapor, not liquid water, due to pore size.
And IIR, eVent pores are also "vapor only", but with a wider functional range.
So any moisture on the inside is from wetting out is condensation, not capillary transport.Jul 30, 2013 at 7:36 am #2010847
Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
I think "wetting out" is just what happens to the outer fabric layer and the "swiss cheese" analogy isn't too bad.
The membrane always gets damp if you're perspiring. Temperature gradient across membrane drives water vapor out. If the outside of membrane is wet, this interferes with vapor being transported out. Thus the outer fabric with DWR to keep water off membrane.
Now, logically, if water is being kept off the membrane, it seems like you could just eliminate the membrane and save some weight…Jul 30, 2013 at 9:44 am #2010896
"I'm pretty sure GoreTex passes only vapor, not liquid water, due to pore size."
No, I agree! But there are a spectrum of breathability versus water resistance, and using the cartoony analogy this would be represented by the hole "size" – basically it is the energy required for a molecule of water vs a droplet with a certain size and corresponding surface energy. If there is damage of some sort then the channels could get bigger. But a really breathable jacket like the Houdini does repel some water up to a point, but at some point if there is enough water so that the surface energy factor goes away, they will go through more or less along the path I described.
Ever for very small pores there is another possible route that is more sneaky. I'm speaking theoretically as a physicist – so it may no apply in many cases, but if you got some chemical on your jacket that did not "harm" the membrane in the sense of abrading it or changing its chemical structure, and so on, but got adsorbed by the water droplets on the surface the right kind of surfactant could lower the surface energy. So it could get in via a sneaky route – water droplets land on jacket, droplets adsorb surfactant, single atoms of water can now get across barrier because they no longer feel the same energy barrier at the surface boundary. This is no doubt part of the reason why you need to keep a jacket clean for it to work its best.Jul 30, 2013 at 12:48 pm #2010950
It seems like you don't really understand what you're trying to lecture us on.
When a jacket wets out it is no longer able to pass water vapor from inside, through the membrane, to the outside of the jacket due to the build up of liquid water on the outside surface. It does not mean that a membrane previously impervious to liquid water is suddenly able to freely pass water through.
The DWR simply keeps water from collecting on the outside. Gore tex will be water proof even without DWR. It won't be any better than a vapor barrier though if the DWR is gone and the outside is wet.Jul 30, 2013 at 1:20 pm #2010966
Nick GatelBPL Member
@ngatelLocale: Southern California
My poncho never "wets out."
:)Jul 30, 2013 at 1:31 pm #2010968
It must be made from cheddar cheese, right?
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