A question about waterproof clothing

[Steve922]

I've just bought a GoreTex jacket. The salesman also sold me a Nixwax treatment for washing  and reproofimg after wearing for a while. Sounds a good idea but...
If Goretex is waterproof, why would it need re-proofing? Ever?   Also, I gather some Goretex clothing has a DWP coating on the outside to improve waterproofness.  What is going on here?
   BTW, the extra treatment which I bought (for £7) is in two bottles: NikWax  Tech Wash  and NikWax Wash-in.
    If Goretex is waterproof and breathable, why the extra treeatments? Either DWP or NikWax ?

[stubill]

This is my understanding of GorTex clothing.


The DWR is applied to the outer fabric by the manufacturer, this is a first defence against water ingress, and to allow the GorTex membrane the best chance of working to it's maximum.


After a while the DWR wears off, and needs to be re-applied, you'll know when this is as water will no longer bead on the jacket and roll off.


Before you re-proof the jacket it's best to wash it in Tech Wash, sometimes after a wash, and a tumble dry (on low) will be enough to reinvigorate the DWR for a while, if it does need re-proofing I wouldn't use the Nik Wax wash in, as I think it blocks the pores in the GorTex, and stops any breathability it has, use the spray on stuff and only apply it to the outer fabric.


That's my take on it, and I've been doing this on my waterproofs for years, other may have a different idea though.

[sussamb]

Wash in stuff works fine on most jackets, some though need the spray on due to their design, my Keela jacket for example is one. 

Goretex jackets need washing occasionally to remove dirt, since this clogs the pores of the Goretex and it's therefore less breathable and more prone to water ingress.  Using normal washing methods destroys the DWR which is why you need specialist or other appropriate cleaners.


This gives some useful advice and information http://www.gooutdoors.co.uk/expert-advice/guide-to-waterproofing-

[NeilC]

Yeah don't rush to replace the DWR with nikwax. Usually the DWR put on by the manufacturer is superior to after-market sprays and washes. So it's best to eek that out for as long as you can and you do that, as per the advice above.


After several wash and dries, it stops working and then you need to reproof.

You're correct that goretex is waterproof and doesn't rely on the DWR for waterproofness. But it really relies on it for breathability. It cannot breath when the pores are covered in water. If it's not beading, it's not breathing. That's why you have to reproof after a while.

The sad truth is that all fabric will wet-out eventually (I think I'm using "wet-out" correctly here?  - the surface soaking up water). Even brand new goretex will wet in sustained windblown rain or where your arms rub your sides etc. It's one reason the breathability of these technologies isn't what it should be.


The situation has got worse since they worked out PFCs are bad for the environment and possibly people too and started with less effective treatments. Patagonia's spin on it is here: https://www.patagonia.com/blog/2015/03/our-dwr-problem/

[NeilC]

Wash in stuff works fine on most jackets, some though need the spray on due to their design, my Keela jacket for example is one. 

Goretex jackets need washing occasionally to remove dirt, since this clogs the pores of the Goretex and it's therefore less breathable and more prone to water ingress. 

Is that true? I heard eVent can leak when dirty but I'd always believed Goretex wouldn't, but would just rather not bead and therefore not breath?

[sussamb]

Goretex is not on the surface of the jacket, it's the surface that has the DWR treatment.

https://www.gore-tex.com/technology/what-is-gore-tex

[NeilC]

Goretex is not on the surface of the jacket, it's the surface that has the DWR treatment.

I know. Not sure what you're getting at though?

[sussamb]

DWR is applied to the surface to stop it from wetting out, you mentioned Goretex would not bead and therefore not breath.   You're getting the two confused. 

Cleaning a Goretex fabric unclogs the pores, this helps with breathability and waterproofness, DWR is applied to the outer layer to help the outer layer, not the Goretex, bead. More info here

https://www.gore-tex.com/support/restoring-water-repellency

[NeilC]

DWR is applied to the surface to stop it from wetting out, you mentioned Goretex would not bead and therefore not breath.   You're getting the two confused. 

Cleaning a Goretex fabric unclogs the pores, this helps with breathability and waterproofness, DWR is applied to the outer layer to help the outer layer, not the Goretex, bead. More info here

https://www.gore-tex.com/support/restoring-water-repellency

Goretex is used to describe the membrane, the whole laminate and indeed the company. I'm using it to describe the laminate here -  I think that's why we're talking at crossed purposes?


My understanding of it is this:


The DWR is coating the fibres of the face fabric. It lowers the surface tension between the water and the fabric to the point where the attraction between molecules is higher than that of water to the fabric. Therefore water molecules stick to other molecules to form drops ("beads") instead of adhering to and running around the fibres. With beads on the surface, most of the PTFE membrane underneath that fabric is clear of obstruction and can therefore breath. But when the DWR is lost the water soaks into the fabric and a layer of water covers must of the underlying membrane. This means water vapor can no longer get through the pores easily, since they're covered in a layer of water held in place by the fibres of the face fabric. That's why the DWR is integral to the breathability and why goretex that wets out is as breathable as a plastic bag.


The question I was asking was about whether dirt could allow water to get through the membrane. We know the pores allow individual water molecules in the form of water vapor to pass through so they're clearly much larger than individual water molecules but liquid water is never individual molecules and are held together by hydrogen bonding which is quite strong. Some types of contamination will break surface tension and go some way to overcoming these bonds but it's going to need to break it down to the point where the groups of molecules are smaller than the pores. I can see this happening under certain circumstances but not sure.


EDIT: even  as I'm writing this and reading the usual explanation from Goretex about how the "pores are too small to let water in but big enough to let water vapor out" it occurs to me that this is clearly nonsense! Water molecules are the same size and if they can get through in vapor they can be pressed through as liquid. Goretex must work differently to the way their little graphics pretend.

[sussamb]

My understanding of it is this:

The DWR is coating the fibres of the face fabric. It lowers the surface tension between the water and the fabric to the point where the attraction between molecules is higher than that of water to the fabric. Therefore water molecules stick to other molecules to form drops ("beads") instead of adhering to and running around the fibres. With beads on the surface, most of the PTFE membrane underneath that fabric is clear of obstruction and can therefore breath. But when the DWR is lost the water soaks into the fabric and a layer of water covers must of the underlying membrane. This means water vapor can no longer get through the pores easily, since they're covered in a layer of water held in place by the fibres of the face fabric. That's why the DWR is integral to the breathability and why goretex that wets out is as breathable as a plastic bag.

Agreed 

[NeilC]

Agreed 

lol. classic definition-of-a-word situation 


however.....turns out a some of it isn't really true anyway. The real way Goretex works is more complex and nothing like those little pictures of vapor coming directly through the fabric.


https://www.scribd.com/doc/66945116/Introduction-to-Waterproof-Breathable-Membrane-Technology.


So it seems that the PTFE layer (under the face-fabric) is a web of fibres with gaps easily large enough for liquid water to pass through, but so hydrophobic that it doesn't. So that's the main method of keeping water out. Then under that is a PU layer which is continuous not filamentous - it does not have pores sized to let vapor out. Any pores it has are too small for that. But it has been made hydrophillic. Sweat, be that vapor or liquid, gets attracted into the PU layer and diffuses through it until it hits the PTFE layer which is dry because of it's hydrophobic nature, and there the water can evaporate. So it's not "breathing" at all really. If the PTFE layer gets compromised by dirt or detergent then it's no longer as hydrophobic and channels form that allow water to pass inwards to the PU layer. Once the top of the PU layer is as wet as the inside, there is no net diffusion outwards and so it cannot "breath" anymore and in fact could start to transfer water the other way but that would only happen if the PTFE layer is significantly compromised. The start of that compromise would be the breakdown of the DWR since that stops water even getting to the PTFE layer in the first place.


So fundamentally, Goretex fabrics are not breathing at all and do not let water just vapor pass though but instead are effectively wicking water to a dry surface. I never knew that.

[ninthace]

EDIT: even  as I'm writing this and reading the usual explanation from Goretex about how the "pores are too small to let water in but big enough to let water vapor out" it occurs to me that this is clearly nonsense! Water molecules are the same size and if they can get through in vapor they can be pressed through as liquid. Goretex must work differently to the way their little graphics pretend.

No it is not nonsense.  A water molecule consists of a hydrogen atom bonded of an oxygen atom which is then bonded to a further hydrogen atom; the classic H2O but actually H-O-H. However this is not the whole story. Because of the electron structure of the atoms the angle between the two H atoms and the O atom is about 120 degrees so the molecule looks like this ^  .  The point is negatively charged and the ends are positively charged - the molecule is a dipole. The +ve H atoms of one molecule can therefore be attracted to the -ve O atoms of other molecule - this is known as hydrogen bonding.  The result is that the water molecules are constantly interacting to form larger structures.  The size of these structures depends on the ambient temperature - the cooler the temperature, the larger the structure.  When water freezes the hydrogen bonds form the water molecules into a regular lattice.  As the water liquefies and warms up, these structures become more transitory and finally breakdown altogether which explains why ice is less dense than liquid water. Typically, water at "room"  temperature is around H32O16; pure steam (the clear stuff from the kettle spout) is H2O. Water vapour is close to H2O so the "molecules" are small enough to fit through the pores whereas the liquid "molecules" are too big.

[NeilC]

No it is not nonsense.  A water molecule consists of a hydrogen atom bonded of an oxygen atom which is then bonded to a further hydrogen atom; the classic H2O but actually H-O-H. However this is not the whole story. Because of the electron structure of the atoms the angle between the two H atoms and the O atom is about 120 degrees so the molecule looks like this ^  .  The point is negatively charged and the ends are positively charged - the molecule is a dipole. The +ve H atoms of one molecule can therefore be attracted to the -ve O atoms of other molecule - this is known as hydrogen bonding.  The result is that the water molecules are constantly interacting to form larger structures.  The size of these structures depends on the ambient temperature - the cooler the temperature, the larger the structure.  When water freezes the hydrogen bonds form the water molecules into a regular lattice.  As the water liquefies and warms up, these structures become more transitory and finally breakdown altogether which explains why ice is less dense than liquid water. Typically, water at "room"  temperature is around H32O16; pure steam (the clear stuff from the kettle spout) is H2O. Water vapour is close to H2O so the "molecules" are small enough to fit through the pores whereas the liquid "molecules" are too big.

Yes I get all that

My phrase "Water molecules are the same size and if they can get through in vapor they can be pressed through as liquid" was a bit loose but fundamentally true. Water molecules are the same size whatever the phase. The difference is the bonding between them, as you point out. Bear in mind piece I was reading was saying the pores are 700x larger than H20 molecules - that's the bit that made me wonder.

The point is, Goretex does not work by merely having little holes that are big enough for water vapor to pass but not liquid.

Turns out, the way it actually works is different and the PTFE layer is not a continuous sheet with little pores in it of just the right size. It's a web of fibres with gaps easily big enough for liquid H20 to pass. And it's not the only layer transporting water.

Read the link above, it's quite illuminating.

[phil1960]

But what about Event, Pertex and ..............
No second thoughts please don’t 

[sussamb]

I just know it works ...