Gearblog! 13 June 2006

Sometimes it worries me that this job has unbalanced me, especially when I fall over on incredibly straightforward paths. Worst of all is the gnawing obsession with breathability or moisture vapour transfer rates that testing gear develops.

No longer can I simply wear a waterproof shell jacket; now I only have to pull one on and my mind is a maelstrom of conflicting analytical judgements - is moisture clearing faster or slower than with the last jacket I used? Am I sweaty? Does it matter?

Oh, that last one's more existential than most gear-testing considerations, so let's just assume that it makes a difference. The problem is that most testers rely on subjective assessment. Lab tests, where the results are available, tend to be about steam and hot plates and weird test rigs that don't bear a lot of relation to a human body.

Steam...

Some manufacturers have used humidity sensors within clothing to measure changes in, well, humidity while the jacket's being worn. Then you can play games with kettles and steam. For what it's worth, steam from a happily boiling kettle will penetrate eVENT - rapidly - Gore-Tex more slowly and most other breathable fabrics too.

What does that mean? Well, when was the last time you produced sweat at temperatures of 100 degrees centigrade? In reality, the only waterproof fabrics I've ever seen allowing steam from a human body are eVENT and Paramo, both after extreme, sweaty exertion on a very, very cold night. I've never seen steam rising from my shoulders wearing Gore-Tex or other waterproof fabrics.

I'm not saying that means eVENT and/or Paramo are more breathable than Gore-Tex by the way, but it's an interesting observation no?

Bubbles...

Meet my new toy, an eVENT bubbler. Okay, it's an eVENT propaganda device, but it's interesting despite that. It's a metal tub that you can clamp a piece of waterproof fabric over, cover in water, then blow through to see if air under relatively low pressure will genuinely pass through the fabric. If it does, you see bubble emerging from the fabric, which is nice.

We're not talking super-heated steam, or high pressure, just air under a moderate pressure. So what are the results? Clamp some eVENT in place and blow through the mouthpiece and you get a steady stream of small bubbles, suggesting that the PTFE membrane that eVENT uses really is allowing air to pass through the fabric.

eVENT fabric in bubbler mode - you can see that medium blow pressure is enough for air bubbles to pass through the fabric and rise to the surface of the water.

When you try the same exercise with Gore-Tex, nothing happens no matter how hard you blow. Yet both Gore-Tex and eVENT supposedly use similar technologies, an expanded PTFE membrane with pores large enough to allow vapour through, but small enough to stop water in liquid form from penetrating.

Gore-Tex Paclite fabric - you can see the fabric doming under air pressure, yet none of the air passes through the fabric because of the PU-based protection layer inside the membrane..

The reality though, is that waterproof Gore fabrics actually have an additional thin layer of polyurethane on the inside of the membrane. It's there to prevent contamination of the membrane which can otherwise cause leaking. PU is used as a proofing coating in waterproof fabrics because it's very hydrophylic, which means it attracts water and moves it outwards.

Gore-Tex XCR - the same result as with Paclite

P Who?

Because the membrane in Gore-Tex is doing the proofing, the PU layer can be thinner than it would be normally, but it still means that water has to pass across it before it reaches the membrane. And as PU isn't air permeable, it can't cross the PU layer in vapour form. That's even more so with Paclite, which has a thicker, hydrophilic layer - the grey liner - that absorbs water as soon as it appears. Try rubbing some moisture into a Paclite fabric and you'll see what I mean. It doesn't emerge instantly on the outside of the garment, so it must be held in the grey layer...

And another one - this is Paramo's directional fabric which allowed air to pass through it with minimal blowing pressure, significantly less than with eVENT because the technology it uses is significantly different. In hydrostatic head lab tests it's not even 'waterproof' but in the real word it works, though the extra liner makes it too warm for some users.

So what does that mean? I'm not saying it proves that eVENT is more breathable than Gore-Tex, even though it feels that way, but it's definitely an interesting insight into the way the fabrics work. The protective layer is present in eVENT by the way, but inside the pores, so it still works as an air-permeable membrane.

Interestingly Gore's Windstopper fabric does pass air in the bubbler test because, as far as I can tell, there is no PU layer on Windstopper. Why, because it's a windproof rather than waterproof fabric, so contamination and leakage is less important. Subjectively, Windstopper and eVENT breathe about the same by the way, which is pretty much what you'd expect.

So what?

Does it matter? I think it does. First, it's about time Gore-Tex was more open about how its fabrics really work instead of claiming that the technology is all about the breathable membrane. Second, it backs up the subjective testing we've been doing where eVENT fabric feels appreciably more breathable than Gore-Tex waterproof fabrics, full stop.

What next? A more durable DWR is what I reckon - it doesn't matter how breathable or not a fabric is, if the outer face fabric gets saturated with rain, breathability is massively reduced at a stroke.

Blimey, is that the time...