Windproof? What is the technical definition of windproof?

[Edward John M]

Asking as I am having trouble with a DIY project for winter. I have no problem with utilising the coffee filter test for my breathable shells but when it comes to making my big winter shell over parka this needs to be windproof not wind resistant and I am wondering what exactly defines “Windproof”?

Also is there a real world difference between the porosity of something like the Goretex membrane and old fashioned fabrics like Ventile/Etaproof and the like or at a certain level they become functional equivalents?

I have a selection of fabrics to work with, some of which are the equal of 3 or 4 filter papers and also some original Ventile which I cannot breath through at all, so 6+ filter parpers I guess

 

[Paul McLaughlin]

I don’t know if there is any sort of widely accepted definition of windproof, or any standard for it. But It seems to me that any tightly woven nylon is effectively windproof: and any fabric advertised as downproof would certainly qualify. It’s one of those terms that is widely used without being well defined. One would assume that to be truly windproof a fabric would have to be airtight, which I doubt you want. What we should say more properly is highly wind resistant, and lots of fabrics are that.

From what I have heard of Ventile, it is more breatheable than gortex is. Goretex has very little air permeability and though has some breathability it’s pretty low. My understanding is that for extreme cold, Goretex and other membrane fabrics are not necessarily the best option, since after all you do not need waterproofness at those low temperatures. But in terms of wind resistance I would think they are functional equivalents. Were I in your shoes I’d be looking at the wintertrekking forum to see what all those folks do.

[Edward John M]

Actually I was chasing a technical definition so I could more easily compare the Non-membrane fabrics to weed out those not suitable. There is a huge range of fabrics out there that may be OK under mild conditions but that may not be storm proof

 

[Greg Mihalik]

“…may not be storm proof”

Careful.  Storm proof is a different kettle of fish.  Don’t confuse the cooks.

[Paul McLaughlin]

As I tried to say – probably I wasn’t clear – I doubt you can find a widely accepted techincal definition of windproof. Certainly there is no legal definition, so anyone can use the term any way they want to, thus it is usless to rely on any manufacturer’s use of the term. “Stormproof” is in the same category. What might be useful to you is to use the CFM rating of the more breathable WPB fabrics, such as eVent, as your standard. Goretex has less breatheabilty – so little that CFM ratings are meaningless for it, and only moisture vapor transmission figures are typically quoted. But if you take the highest CFM rating for eVent and use that as your maximum acceptable CFM I would say you can’t go far wrong, as that should be a lower CFM than you really need for effective windproofness. Of course, then you need to be able to get CFM numbers for the other fabrics you are considering, which may be easy – or not. Also, by perusing the various windshirt threads here on BPL and reading only the posts by RIchard Nisley, you will pick up some useful numbers to consider.

[Edward John M]

Yes “Stormproof” implies a large stiffness factor inherent in the fabric as well as resistance to wind penetration

I have Richard Nisleys article open in front of me and I was going to assume that anything with a porosity lower than 5CFM would be considered highly wind resistant but would that be good enough to resist winds of 100kph?

The L28 Ventile I have here tests to 0.4 cc/cm<2sec, 0.98 mbar which converts to 0.74CFM but that needed to be doubled to be considered windproof enough for Everest / Antarctica in the 1950s.

Were the British and Australians being too conservative back then? Also L-28 Ventile is heavy at 280 / 300GSM

Way back in the late 1970s I had one of the REI  K-2 ripstop clown suits, it was marginal in a strong Scottish blow and I thought then that is should have been a double layer. For my Alaskan trip I want the best I can make consistent with my lightest pack weight

[Roger Caffin]

any tightly woven nylon is effectively windproof: and any fabric advertised as downproof would certainly qualify.
Not in my book. ‘Downproof’ fabric by definition allows air through.

Were the British and Australians being too conservative back then?
Who knows – but I believe they survived the winds.

Many of us have said it many times before: UL idealogy is a great idea on a warm sunny day, but don’t be so stupid at -10 C and 60 kph.

Cheers

[Paul McLaughlin]

As an anecdotal data point, I have pants made of EPIC fabric which i have found to be windproof in winds which were too strong for me to stand in without having something to hold onto. Mr. Nisley may have measured cfm on some EPIC fabric, so that mightgive you another reference. I have had similar field experiences with goretex – both first and second generation. I have heard that the first gen stuff was close to what eVent is now in terms of breatheability but i am not sure i have seen numbers on that.

[Edward John M]

Anecdotally my Goretex is more “Windproof” than my Ventile but the experiences being decades apart it is hard to make a definite call on it and while I’ve not personally had the poor experiences with Goretex that others report, but my experience bottoms out at -25C and below that temperature appears to be where the membranes stop venting vapour

[Edward John M]

Just another thought.

CFM ratings are taken at a pressure that approximates a 30mph wind, a gentle breeze really . What happens when wind speed increases to something approaching a fast snowmobile run ? Say 65mph / 110kph?

From my motor cycle riding days a couple of hours at 110-klicks can be a lot colder than a few hours at a much lower speed

[Paul McLaughlin]

Well, heatloss due to wind is somthing you will have regardless of how windproof your shell is, because there is still convective heat loss. It’s just that with an effective shell the convection is occurring off the outside of the shell rather than somewhere inside your insulation. So higher wind speed equals more heat loss no matter what you are wearing.

[Edward John M]

Granted but higher wind speed must also mean greater penetration too, therefore the greater the wind resistance the lower the overall heat loss.

So in my particular case I need to know for my own DIY

If a single layer of fabric at a particular weight will do then I save weight by not adding a second layer. My own Ventile at ~ 2CFM is one the heaviest,tightest and most wind resistant  of the Ventile family but I can with difficulty breath though it. Wincol fabric is no longer made but it was heavier and tighter again and was measured at 0.66CFM and I’ve not seen it since I was about 16YO, The Australian navy used it in windproof jackets for deck use and I remember the labels

Goretex measures 0 I think and isn’t that regarded as windproof

[Roger Caffin]

Underlying all this is a perversion of the English language driven by commercial marketing organisations, driven by unethical behaviour and greed.

‘Waterproof’ apparently no longer means waterproof, just whatever the vendor needs to be able to make a claim. ‘Well, it only leaks a little bit, so that is close enough’.

‘Windproof’ apparently no longer means windproof, just whatever the vendor needs to be able to make a claim. ‘Well, it only passes a little bit of air, so that is close enough’.

Let us have no more fiddling with the facts or the truth. If any water gets through, the fabric is NOT waterproof. If any air gets through, the fabric is NOT windproof. ‘Waterproof/Breathable’ is a contradiction in terms and basically it is a lie.

But I doubt my comments will have any effect on the vendors.

Cheers

[Edward John M]

Howzabout effectively windproof?

Windproof enough for bushwalking and/or hiking is not windproof enough for the Antarctic/Arctic or the high mountains so we do need some sort of technical defining of adequacy.

I think Wincol fabric would be close enough but that level of resistance isn’t easy to achieve with UL materials

[Roger Caffin]

effectively windproof?
Weasel words – otherwise known as lies.

Try a yellow PVC yachting jacket and pants. Now they are both waterproof and windproof.

Btw – I have far less objection to ‘water-shedding’ or ‘wind-blocking’. You have to given them some wiggle room.

Cheers

[Paul McLaughlin]

Edward – in the most precise technical sense you are correct I’m sure about the higher wind speed causing some slight difference in penetration and thus heat loss; but that would be so tiny compared to the additional convective heatloss from the exterior that it can be ignored. Which is applicable to a lot of these questions. We’re not going to arrive at an accepted definition of windproof or of wind resistant, but it’s reasonable to think that it’s feasible to come up with a CFM rating that would signal an acceptable level of wind resistance.

Now obviously it’s quite easy to find a completely windproof fabric – by anyone’s standard – by going with something intended to be fully waterproof and NOT breatheable – as in Roger’s vinyl slicker, or with coated nylon that has a decent HH rating. But that’s not what you are after, clearly. So it seems that perhaps what you are asking is how low a CFM can you get to and still have some functional breatheability – functional at the low temperatures you intend to deal with?

I’ll make a suggestion here – what I would do if I wanted a clear set of data is to get together some samples of possible candidates, and send them to Richard Nisley with a friendly request for him to test their CFM. Once you have that, you can pick the one you like the numbers on, or if none of them look good, get some more candidates, and keep trying.

[Edward John M]

“So it seems that perhaps what you are asking is how low a CFM can you get to and still have some functional breatheability – functional at the low temperatures you intend to deal with?”

Yes I think I was phrasing wrongly.

Re-reading the excellent post by Richard Nisley [ A revised Paradigm] I think anything about 2CFM should probably be considered windproof enough. but in this instance I think lower would be better.  Doing some of his coffee filter equivalent testing I may be able to find a combination here that works “well enough” without being so heavy I would leave it behind due to excess weight.

You are correct, I should contact Richard and arrange to send some samples to him

 

[Edward John M]

I did contact Richard, but because I’m asking about fabric in my existing stash and not generally available to the general BPL community he understandably seemed to decline.

Back to the suck test then and hope for the best

[Dale Wambaugh]

Any membrane fabric will be wind proof and the “breathable” description for those fabrics is about vapor transmission, not airflow. CFM data are the thing to look for and very hard to find. Other than Nisely’s reports here I’ve never seen CFM info.

[Edward John M]

Gerry Cunninghams little DIY book had some old information. Ol’ Gerry understood how important windproofing was. But none of those fabrics are really available now or relevant at the LW end of the spectrum

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