Windshirts — Breathability vs. Wind Blocking

>For those who also have had different windshirts, please share your experience as well. If there is a trade off, how do you draw the line?

My windshirt is a Montane Aero smock (no hood; XXL: 3.2 oz), made from Pertex Quantum, and there is no trade off–it stops the wind completely and is highly breathable. I've worn it in below-freezing gusts strong enough to knock me over, but didn't feel any colder when the gusts hit. I put it on over a soaked shirt when I got chilled and dried out the shirt in 15 minutes while still hiking. I've never had any condensation on the inside. The only downside is that it is only water resistant, not water proof.

Unfortunately, it seems to have been discontinued in favor of the Featherlite smock, made from Pertex Microlight, and I'm not sure how well that performs. The general recommendation for the Aero is to go up a full size from what you normally wear; it worked for me.

Hi, Ben. The Houdini does a great job blocking wind. The balance that it provides over all the attributes one could want from a windshirt is pretty stupendous. Very good breathability and wind protection for the 3.5 oz. weight. I have tried other windshirts (older Golites mainly), and I agree with your observations; they block wind very well but are not very breathable. The Patagonia maintains a great balance. The amount of extra warmth it gives me on hikes actually really surprised me at first. It is so so soft on the skin yet shrugs off the wind very well. I find it an invaluable part of my kit.

I still remember some VERY heavy and cool winds I experienced while above treeline on East Baldpate in Maine last summer. I began to feel chilled, put on the Houdini, and felt great for the rest of the hike. I was all smiles.

I own a Montbell U.L. Wind Jacket and the Houdini. I'm guessing my Montbell is similar to the Helios. It isn't very breathable. Both seem to block the wind equally well. The Houdini is definitely more breathable and seems more water resistant as well. I'm not sure how that's possible, though a recent post suggested that the fabric of the Houdini might be Epic like. I've had the Houdini for a year now and the Montbell for 2. I wore the Houdini skiing this winter with winds above 40 mph and it did it's job. You are absolutely right, there is a point where a windshirt could be too breathable. The Houdini is not there in my opinion.

Here's my basic comparison:

Breathability:
GoLite Ether (04/05 old model nylon/acryclic) < Marmot Ion (Quantum) < Montane Featherlite (Microlight)

Wind Resistance:
Montane Featherlite < Marmot Ion < GoLite Ether

One important factor I like to keep in mind is the "sealability." The Ion has a short, loose bottom hem where cold air likes to sneak in. The Featherlite is flappy in wind, which can make for an unpleasant bellows effect in really stiff wind. The Ether, however, has wonderfully snug cuffs and hems that really keep a nice seal. If I'm facing cooler temps where body heat is more important and I'm less likely to sauna myself, I'm willing to take the Ether.

If I'm looking at warmer temperatures where I'll need more breathability for higher temps or higher exertion, the Ion and Featherlite come in.

-Mark

Thank you all for your insights!

Ben,
Sorry to chime in late..
I rank my windshirts on a spectrum, with air permeability (AP) on one end, and wind-resistance on the other end. Air permeability is the inverse of resistance to wind- how could it be otherwise?
So, most to least air-permeable, here goes..

Houdini
Montbell Wind blaster in 'Drytec'
eVENT (I know, not a light windshirt, but it is AP)
Trash bag with hole for mouth
2006 Marmot Ion

Im selling or retiring all except the Houdini.

Ahh, the trash bag. Now that is a gorgeous piece of gear!

> One important factor I like to keep in mind is the "sealability." The Ion has a short, loose bottom hem where cold air likes to sneak in. The Featherlite is flappy in wind, which can make for an unpleasant bellows effect in really stiff wind.

Good points Mark! My Featherlite is a fairly loose cut and it can flap loudly in strong wind. But it's sealed well at the waist with lycra. Breathability is excellent.

The cut of my 2006 Ion is very close so there's no flapping. The wrists have tight elastic, but the waist is open so I found the breeze coming up when riding my bike. My solution was to open the hem at both hips and put a couple inches of elastic there. I have virtually no sewing skills but this worked out well. Alas the breathability of the 2006 is poor; it's not really Quantum as advertised.

What I really want is the close cut and full zip of the 2006 Ion but made of real Quantum and with a lycra seal at the waist. The Montane Jetstream looks promising. Anyone have experience with that? Or know of another choice that would meet my needs?

Ben said in part: “I understand that the Patagonia Houdini is even more breathable than the Marmot Ion. Those who own a Houdini and perhaps something esle present or past — pray tell — does Houdini's superb breathability come at the expense of wind blockage? If so, then I wonder at what point chasing after maximum breathability would result in a windshirt that no longer blocks the wind optimally???”

Cubic feet per minute per square meter (CFM) is a measure of the wind resistance or air permeability of a fabric. The higher the CFM, the greater the volume of air passing through.

Traditional barriers like H2NO, Gore-Tex, eVENT, Triple Point, Entrant, and other respectable waterproof breathable technologies all have a 0 CFM rating. If you are just sitting still or doing camp chores a 0 CFM garment will block all wind and keep you the warmest. Both eVENT and Gore-Tex Direct Venting achieve this with a pore size of about .2 microns.

With the advent of soft shells and more breathable fabrics, the air permeability argument becomes complicated, sometimes heated. If you are backpacking, you can afford a bit of convective heat loss. You need more breathability to move the extra moisture you create through exertion. And a fabric with 0 CFM doesn't provide it. Fabrics that measure as much as 5 CFM are still functionally windproof: that is, you don't feel the breeze come through. And they afford much greater comfort with the high exertion rates during backpacking. Popular wind shirts, like the Patagonia Houdini, fall into this class as do the best soft shells. The average pore size for this class of fabrics is about 20 microns or 100x times larger than eVENT. Any larger pore size will result in more than 5 CFM. After 5 CFM you can start to feel the wind through the fabric.

To put the Houdini pore size into perspective: it is about ¼ the diameter of a human hair; it is about 10x smaller than the finest water mist; and it is about 100,000 times larger that a water vapor molecule.

In my opinion, the Houdini’s encapsulated silicone micro-fibers make it the best the best wind shirt on the market for thru-hikes and expeditions because there is no need to periodically renew the DWR for water resistance. For conventional trips of a week or less there are many excellent alternatives such as the Montane LiteSpeed, etc.

Richard, I learned from your latest post, as I always do. 5 CFM is the limit of functional breathability, but I CAN breathe ever so slightly through my eVENT jackets, a Teva, an ID, and a Japanese model. EVENT does not have a solid sheet of plastic like goretex, so it is porus, right?

Right.

Nextec 4 Summit nylon has the almost identical pore size to eVENT, as does Gore WindStopper. Consequently, you should experience the same breath test resistance with all three fabrics/membranes.

You can move air through these fabrics/membranes but, the average person cannot perceive wind convection.

I'm watching this thread and am getting some good info! Richard is saying that the Houdini has got encapsulated silicone micro-fibers and doesn't need DWR reaplying.Why has Patagonia added a Deluge DWR finish if it doesn't need one? To make it more water repelent?

Just becuase I'm curious, and not to get off topic…but where does the OR Ion rank in breathability and wind blockage? I just picked one up for dirt cheap, and Im just interested in the expert opinions here. So please….opine.

Richard — Thanks for the info!

Now, I am very curious about the CFM rating of my 2007 Marmot Ion. It is definitely something more than 0, but how much more? Hmmm….

I too am interested in the characteristics of the marmot ion. I like the houdini much more but can get the ion new for 20 dollars. Is the houdini that much better to the point where i should still go for it?

That's a great deal; and lowers the resale value of mine!

Jon:

Much depends on how or where you balance between breathability vs. wind blocking.

IMO, if $20 gets you the 2006 Marmot, then save your money — unless you intend to wear this jacket only at the beginning of a hike, and then at the end when you are at rest.

If $20 gets you the 2007 Marmot, then I think that can be a very good thing indeed. For me, the primary reason for getting a wind jacket is to block the wind — esp. if the wind should start howling when I am at rest. The degree of breathability just enables me to defer taking off the jacket when hiking along. But no matter how breathable, considering that I will sweat even with just a tee shirt on, I will want to take the jacket off eventually anyway.

But if the wind jacket is too breathable — such that I could feel the chill at the end of my hike, then that to me would defeat the purpose of wearing the jacket in the first place!

My first wind jacket was the old barely-breathable Golite Helios. I was always amazed at how something so utterly thin and light could make such a big difference in warmth when cool winds were blowing! With the 2006 Marmot, I could feel the difference — the Marmot was a bit more breathable, and didn't block out as much wind. Now that I have the even more breathable 2007 Marmot Ion, I feel like I have achieved the right balance for my purpose — i.e. any more breathable, the jacket may not heat up enough for me when at rest.

So, if your objective is maximum breathability — say for bike riding — then you probably should go for the Houdini. But if — like me — wind blocking is primary and breathability — while desired — is only secondary — then maybe the Marmot Ion is the better choice…

I put together a table of representative CFM values for common outdoor clothing materail.

If anyone on the forum has values to add, please post them.

Richard,
some comments on your table.
First, I think the value for windstopper and eVENT is not completely correct because these are somewhat air permeable (as has been shown by a bubbler test). I don't know exactly what the CFM-rating for these two is but info from Marmot indicates that for Windstopper it's less than 2 and windstopper and eVENT probably have similar ratings.

For soft shells like powershield, the rating is 10-15 CFM as you stated although I have a number as low as 6,42 so it . For fabrics like schoeller dryskin, it's more like between 15-20

Tom: Marmot’s International site correctly lists Windstopper at 0 CFM and then later contradicts the first statment by saying it is <2 CFM; see Marmot CFM

Most sites correctly list it at 0 CFM. Examples are as follows:

Example 1

Example 2

Example 3

I suspect that the apparent Bubbler contradiction is a result of a fractional CFM test results that are rounded to 0.

I updated the table to reflect the 6.4 CFM for Polartec Power Shield plus added a few additional entries.

In order to approximate the CFM for an unlisted garment you can do the following:

1. Suck air through the unknown CFM garment.
2. Extrapolate by sucking air through the closest reference material found in the table.

Richard,
I assume the CFM test is done at a substantial pressure differential. Doing this test myself I find that eVENT is gas permeable, with a CFM > 0 as shown in your table.

Heres what the eVENT site says about vapor (gas) transmission:
"We could mention the exceptionally low "Water Vapor Resistance" (RET) of eVent fabrics. Or, we could talk about how much higher our "Moisture Vapor Transmission Rates" (MVTR) are in laboratory tests…It's that simple. eVent fabrics let the sweat out.™"
http://www.eventfabrics.com/eVent_technology.php

Please take a look and consider revising your table with this new information.
Thanks again for organizing and simplifying all this fabric technology for us; I have learned a lot from you.

Richard,
a few more remarks:
As Brett says, air permeability of eVENT is better than other waterproofs. I have figures ranging from 0,1 to 1,3 CFM with with a mean of about 0,3. Since eVENT and Windstopper are very similar, I guess these numbers can also be used for windstopper. I would also add Breeze Dry-tec in this category although I have no numbers. I also have numbers for a sort of air permeable gore-tex but they are not expressed in CFM.

My other remark is about fabrics like powershield. Due to the way they are constructed, the level of air permeability can be varied and I think it's better to give a range than a precise number. The 6,4 is a number given by Polartec, but in some other documents they give a number of 10. From fall 2007, some garments will be made from a new Powershield, Powershield O2, which is supposed to have a cfm of 50.

Based on the 'percent of naked' document of Patagonia, I guess air permeability for schoeller dryskin is more between 15-20.

Brett-Please reference Waterproof Breathable Fabric Technologies: Definitions

Breathability or WVTR is measured by testing the RET, amoung other methods. This is a different type of measurement.

Wind resistance is measured by testing the air permeability. This was the original thread subject and what my table addressed.

Tom-It seems logical to me that the CFM for eVENT is greater than 0 but I could never find a reputable test reference. Do you have a link to a test reference?

Richard,
although I haven't got a direct reference, you can take a look at this (hope the URL works). For a better lay-out go the image on top of the page:

eVENT

Hmmm, for some reason, it doesn't work. Have to work this out.

BTW, Windbloc has an air permeability of 0. It's windstopper you have to put in the same row as eVENT.