Autoxfil wrote:

FortMental wrote:I don't understand this whole concept of breathability.... maybe someone could help me out here:

The vapor concentration near my skin is nearly 100% when I'm hiking with a pack on. If it's raining, that means the vapor concentration in ambient air is also close to 100%. So, how does vapor leave the space between my skin and the jacket?

It is much warmer inside the jacket than outside. The temperature gradient helps signifiantly - as long as the DWR is up to snuff so the membrane doesn't wet out. But yeah, it still doesn't breathe much.

This is my understanding as well. Temperature difference leads to a vapor pressure difference leads to the sweat passing through the membrane where depending on temperature and humidity it condenses and (if the DWR is working) drips right off you.

If it's too warm and humid for the jacket to breathe, leave it at home and bring an umbrella.

But at the membrane interface the humidity is not 100%, because your jacket is warm(ish).

FortMental wrote:%100 humidity means %100 humidity. Regardless of temperature, the ambient atmosphere's capacity to absorb additional water vapor is ZERO.

So the vapor condenses into liquid form, no?

laws of physics courtesy of marketing suits

In the west, I primarily use my eVent jacket when we have sudden snow squalls in transitional times (late spring, e.g.). The jacket keeps the snow from wetting my clothes, and does allow enough breathability when the temperature is not too high. Else I just keep a totally waterproof poncho or jacket in the pack (if the weather looks at all chancy, I'll have both, plus a totally breathable windshirt).

If there is any time when you will have to sit a bit with the snow flying about, the GoreTex or eVent will usually be able to keep up with your body's sweat production.

In the west, snow or rain often falls from a place of saturation, through much drier air before it hits you.

anita wrote:where's this great deal? I want one!

Just a friend selling locally, not store or anything.

FortMental wrote:%100 humidity means %100 humidity. Regardless of temperature, the ambient atmosphere's capacity to absorb additional water vapor is ZERO. 100 degrees inside, 0 degrees outside; it's irrelevant.

Vapor pressure. heat pumping, temperature differentials........when we leave it to marketing to explain the science of a matter, even the simplest concepts get distorted into BS.

Unfortunately, marketing is doing a better job of it than you. 100% humidity just means that the partial pressure of water in the air has reached saturation, which varies dramatically with temperature. If the temperature at your skin surface is about 80F, and the ambient temp outside is around 50F, the vapor pressure of water at saturation is more than twice near your skin as it is in the outside air. Which means there will be water transport from your skin towards the colder air.

Now, what happens on that magical journey can make a big difference. Temperature doesn't just instantly drop from a nice toasty 80F on the inside of your outermost layer and the chilly outside environment. There are gradients. Which means that the vapor-carrying capacity of the air will decrease. The results? You already knew that--condensation. In your insulating layers, and on the inside of your shell. As certain posters here on SP are fond of pointing out, when the WB layer of your shell gets wet, vapor transport is compromised. I don't know that it actually shuts down, but I would buy into a decrease in performance unless someone could show me some experimental data proving otherwise.

Whether it shuts down or not, the amount of water that stays inside your shell is basically the difference between what your body produces, and what the shell can transport. This is a good argument for having as breathable an outer layer as possible. But you already knew that (I did read your later post on that topic).

Of course, this all leads to another physically accurate marketing tidbit that proves to be less than we would be lead to believe: wicking. Doesn't it sound great to have wicking layers that take all that horrible water from one place to another? Sure, if there's some place for it to go. But if the water has no place to go except the tiny openings at your sleeves and neck, how does it help? Yeah, it dries faster, I think. But still, not nearly as awesome as it sounds.

Don't really care about a physics lesson here but I do wear Paclite shells. Not because of how well it breathes, but rather, because they're light. I generate a lot of heat when I climb so I wear soft shells most of the time and only put on the Paclite shells when it's windy or raining. That it breathes at all is just an additional benefit for me.

Moisture transport through membranes is driven by vapor pressure gradient and is NOT stopped by a high external RH alone (although it is a factor). You can expel moisture into a 100% humid environment anyway. Anybody who has exhaled during a cold rain has witnessed this. All it takse is heat. Once moisture reaches the outside of a membrane, it doesn't have to be absorbed into the air. It can re-condense and wick away through the fabric face, it can steam off if the temperature gradient is dramatic, or, if the humidity is below 100%, it can just blow away as vapor.

Gore Tex, by definition, requires very high internal humidity for it to rapidly transport moisture because it is backed by a hydrophilic monolithic PU membrane (which protects the PTFE from skin oils and abrasion). The PU has no continuous pores so contrary to marketing or popular belief, moisture vapor does not pass through it. Moisture transport is accomplished via solid state diffusion. Moisture condenses on the inner face of the PU, diffuses on a molecular level through the PU, and then vaporizes again from the outer face of the PU (where it can escape readily through the PTFE layer).

Some membranes eschew the PTFE layer for cost reasons (MemBrain, Hyvent, et al) and use just a single monolithic layer of PU (laminated to nylon). Because the fabric they are laminated to has a much larger structure and a smooth finish on the yarns, the PU is necessarily thicker than the PU which is laminated directly to the micro-rough surface of a PTFE membrane. The solid state diffusion through PU is relatively slow so making that PU layer thicker is very detrimental to moisture transport performance, which is why GoreTex clearly breathes better than MemBrain.

Microporous materials such as eVent (oleophobic PTFE with a tricot protective lining), Entrant G2-XT (microporous hydrophobic PU), and Rainshield/3M Propore (microporous Polypropylene sandwiched between two non-woven PP layers) DO allow vapor to be transported directly through the fabric which also means they can transport moisture much sooner (before inside RH is high) and thus keep you drier.

Still, eVent is a waterproof/breathable membrane with very low air permeability so it won't evacuate perspiration as quickly as, say, Shoeller Dryskin softshell, but it definitely outperforms Goretex (and, unlike a softshell, it actually keeps rain out). Likewise, Goretex definitely outperforms PU-only membranes like MemBrain. However, PU-only membranes (like MemBrain) are lighter weight, stretchier, more durable, and less costly than GoreTex.

The main problem with eVent is cost (just as pricey as GoreTex) and weight (heavier than GoreTex). Because of this, many mfgs try to cut weight by excluding venting options like pitzips. They market them claiming eVent works so well you don't need pitzips. Well, I've worn softshells where I wished I had pitzips so really, that's bullshit.

GoreTex is still a pretty good compromise of durability, breathability, and weight, but it comes at high cost and won't be good enough for some. Personally, GoreTex works great for me. I have a number of items in PacLite and ProShell. I can't really tell the difference in breathability.

In summary, membranes DO work (just not usually the way marketing suggests), and they have a limited range of functionality, outside of which, you need to vent or limit activity levels. Each person is different and perspiration rates will vary so for some people, even eVent won't be good enough whereas others will be happy in MemBrain.

Well I agree with FortMental that marketing can drive madness, but actually even if it's raining, it doesn't mean the relative humidity around you is 100%, it means the relative humidity at the altitude where the rain actually forms is 100%. In theory where you are standing, the relative humidity could be anything. If this wasn't true, then if you accidentally got wet in the rain, and finally stood under a shelter, you would NEVER dry off if it's still raining

I have a GTX paclite shell as my "summer" waterproof outer layer. It works great in that its waterproof and with the pit zips and chest vents it ventilates extremely well. All zipped up (in cooler weather) it feels comfortable. I prefer to use it with a long sleeve shirt under because the material feels plasticky against the skin.

For Hiking Paclite is the way to go IMHO. Packs small and its waterproof. There are other options but paclite is probably the best value.

I have heavier duty shells that I use in winter (skiing) but the paclite should work well in cold weather too its just that for skiing I want a tougher jacket that is durable against possible contact with rock, ice and vegetation.

Only place I have found Goretex/Event or any other "breathable" garment to be useful at all is when you are essentially sitting or at best SLOW walking or maybe paddling a kayak. Exception is blowing snow.

Otherwise carry/use a poncho or wind shirt as they are far more effective depending on conditions.

Heck there have been whole summers when I never even take a "waterproof" shell or poncho with me at all even on week long trips. If it rains strip down and move your butt. Also, wear polyester fleece. If its soaked, pull it off and shake the water out and viola its warm again. If its pouring well, you probably aren't moving anywhere during the summer anyways besides sprinting OUT and to your car.

Throw up the tent when you stop as you have to throw it up anyways. If backpacking, use a poncho. One that goes OVER your backpack for maximum weight savings and venting options.