How does GoreTex work?
GoreTex – That miracle fabric which almost every outdoor brand uses to make their kit waterproof.
And for good reason. It’s lightweight, breathes well, and it’s durable. Better still its backed up by a guarantee, which is always a good sign.
Why would you want anything else?
Well there are reasons. PFCs are one. And honestly, do you even need a breathable waterproof in the first instance? But those are topics for more discussions.
For now I’m going to go out and say it. Plastic based waterproof coats, regardless of brand are not the miracle solution to your staying dry needs you thought they were.
And why is that? Well its quite simple. All plastic based waterproof coats work on the concept of their DWR coating working.
So how does GoreTex work? Let me explain and remove the jargon and mystery.
The basics of how GoreTex works
In most plastic based waterproof jackets you have three layers of fabric (Diagram 1)
The soft inner layer -which sits next to your skin on the inside
The GoreTex Layer– this is the GoreTex or similar fabric
The Ripstop Outer Layer – This creates the durability, and is a ripstop fabric
That silver fabric you see on the inside of your coat is not Goretex. Its the backing layer. Goretex membrane is a very thin piece of fabric, and if worn next to your skin, it would get damaged quickly.
The three layers are then bonded together using heat to stick them to one another.
Now in a lab environment, if you wanted to test the air transfer (how well it breathes) of this garment you would find it performs very well. Moisture would pass through effortlessly (Diagram 1). Perfect, sew it up into a coat and you have a happy customer.
But life isn't a lab
But what when it rains? You know, the very thing you purchased the coat for in the first instance!
Well here is where it gets interesting.
When it rains the following happens.
Water absorbs into the ripstop fabic. Spreading itself over its surface area and saturating the ripstop fabric. It doesn’t go through the GoreTex, as that does its job very well. But the vapour which is passing through the fabric hits this barrier of water and has no place to go (diagram 2).
After a short while your sweat starts backing up and soaks you from the inside. This would feel like the jacket has leaked, but in reality is hasn’t.
Along comes the DWR coating!
But fear not. Durable Water Repellency to the rescue (DWR for short).
This coating is like a coating sprayed on at the point of manufacture. It allows water to bead off, but air to pass through.
So you thought.
Well why has your waterproof jacket started to leak?
One of two reasons:
Your DWR coating has become dirty. Once dirty, the DWR coating gets flattened.
Reasons your jacket is leaking
Your DWR is dirty
When your DWR coating gets dirty, with body oils, mud, engine oil – waterever you have managed to get on it ,which isn’t rain water, it will stop performing. A few patches of DWR here and there are not an issue, but if your jacket isn’t beading, its not breathing. Therefore its time to give it a wash.
Your DWR is has worn off
Your DWR will eventually wear off. DWR treatments generalls have a wash out rate of 20/80. That means, after 20 washes, 80% of the DWR coating remains in place on your jacket.
After a high amount of wear, re-coating is helpful. However after some years there will be a point where no amount of re-proofing works. The shop purchased re-proofers never really achieve the same result as the consistency applied in factory.
To wrap it up
I really hope this has helped to explain GoreTex and DWR coatings in a simple and concise manner. It’s really quite a simple idea, but the technology of GoreTex only works on outdoor jackets if it’s combined with DWR coatings. Peversely, DWR coatings are also harmful to the environment and wear away after time leaving you with great technology, that performs poorly without its essential sidekick (DWR).
However, when it comes to waterproof fabrics, there isn’t much choice if you want to buy a breathable, waterproof jacket. And anyway, most people will never use a waterproof enough for it to wear down quickly.