I think that the answer is that the sweat from your body escapes as moisture vapour not actual water eg drops of sweat - moisture vapout transmission - (MVT)is the scientific method used to rate how well jackets do this.
The DWR keeps moisture in the form of water (rain / snow) from wetting the actual material which in turn compromises how effecticely the garment can let moisture vapour escape through the material.
If this is not entirely correct I'm sure somebody will come along to provide a better explanation.
My initial worry about using a wash-in with Paclite is similar to yours; I'm not sure what effect the proofing will have on the black Paclite inner face coating. My understanding is that this coating replaces the scrim on 3-layer GTX, and is used to act as a buffer layer, allowing water vapour to condense to liquid so as to pass through the PU protective layer on the GTX membrane. Since this layer is continuous, rather than the discontinuous nature of the face fabric, proofing it may result in a continuous waterproof layer, thus preventing the Paclite from breathing normally.
I must stress that this is purely speculation on my part, and NOT based on experience.
I'm sure that the PU/GTX membrane won't allow liquid through only vapour. The inner layer of a laminate may act as a buffer and hold moisture vapour but once that vapour condenses it won't pass through the fabric.
My experience is that applying Wash-In treatments to Paclite doesn't affect the breathability.
I have a Patagonia "Ether" Paclite jacket.The care label says to wash in powder detergent!From what I've read on this Forum I've ignored this and used Tech Wash.Annoying when you can't trust the manufacturer's advice.
As I understand it, the PU protective layer on GTX won't allow vapour to pass (it's not a microporous gas permeable layer). It has to take in the water vapour (either by direct adsorption or vapour, or by absorption of condensed water), transmit it through the hydrophilic PU layer, and then evaporate it on the other side through the gas permeable Gore-Tex ePTFE membrane. Granted, liquid water cannot pass through either the PU protective layer, or the Gore-tex ePTFE membrane (at least at reasonable pressures).
That's why the Gore-tex laminate behaves more like a PU coating than a plain ePTFE gas permeable membrane.
My concern was that proofing the PU layer might reduce its ability to adsorb water vapour or absorb condensed liquid water.
I'm reassured by your experience with proofing Paclite, Chris. Thanks; I'll stop worrying about it...
My understanding is that the PU layer is hydrophilic and transmits moisture vapour but won't transmit liquids. The rate of transmission is slower than with the Gore-Tex membrane, hence a reduction in breathability compared with plain ePTFE.
I tested the original Gore-tex, without the PU layer, and it was extremely breathable. It also failed abruptly - in a November storm on Styhead Pass. I was soaked through in minutes and had to abandon as ascent of Great Gable and get down to Wasdale Head to warm up.
eVENT doesn't have the PU layer which is why it's more breathable. However it is treated so it doesn't fail drastically.
The point I was trying to make is that PU is a solid. Gas/vapour cannot pass through it by simple physical means; there are no pores to allow gas to pass. This can be demonstrated by eVENT's bubbler units, showing how eVENT allows gas to pass, because, as you say, it does not rely on a PU layer to protect its ePFTE membrane from contamination by body oils. PU-protected Gore-tex doesn't bubble. Gore-tex Exchange will bubble, because it's a genuine, gas-permeable ePTFE with no PU layer.
So, in order for water to pass from one side of the PU layer to the other, it must pass into the PU layer. There are two possible mechanisms for this:
adsorption: where the water vapour molecules enter the PU layer directly
absorption: where the water vapour must first condense to liquid before it can enter the PU layer.
I don't know which mechanism is dominant.
I'll guess that, since the PU layer is hydrophilic, the water molecules form weak bonds with the molecules of the PU layer (probably hydrogen bonds). By means of diffusion, the PU works to transport these water molecules from one side to the other, where they leave the surface of the PU layer, and pass out through the pores of the ePTFE membrane. That explains why the 'breathability' of PU coatings is dependent on the temperature and humidity gradients between the two sides; these properties drive the diffusion. Note that, since this mechanism is at the molecular level, it makes no sense to talk about vapour or water.
Google raises some useful looking hits (e.g. "Waterproof Breathable Polymeric Coatings Based on Polyurethanes Jassal et al. Journal of Industrial Textiles.2004") for "water transport" "hydrophilic polyurethane"
but they all seem to end up at fee-paying article reprint sites. I need to do some more research. But not tonight...
Have I taken this thread too far off topic yet...?
PU can be microporous or hydrophilic. However the PU in Gore-Tex needs to be hydrophilic so as to be a complete barrier to body oils. Captain Paranoia, I think your diffusion theory is correct. That's how Sympatex, a hydrophilic polyester membrane, works, the water vapour molecules transported along a chain of water loving molecules in the fabric.
I think temperature and humidity gradients are the driving force for all waterproof/breathable membranes and coatings, not just PU ones. Without pressure there is nothing to make the moisture move through the fabric. That's the main reason why waterproof/breathable tents don't work well in humid weather - there just isn't enough pressure to force the moisture through the fabric. (I've found this with both Gore-Tex and eVENT tents).
