Restored windshirt discussion

This thread was hacked but has been restored.
Roger

[James holden]

while the reviews are fine … it should be noted that some of these reviews are by someone “sponsored” by the brand …

the other thing is that your “wind jacket part 2” article is exceptionally misleading … richard states quite clearly that in his opinion an “ideal” windshirt for active use has a CFM of ~35 or so

not the <10 CFM you claim

here is the original thread

https://backpackinglight.com/forums/topic/95378/

;)

 

[Andrew Priest]

I just read the postings you linked in relation to this comment:

the other thing is that your “wind jacket part 2” article is exceptionally misleading … richard states quite clearly that in his opinion an “ideal” windshirt for active use has a CFM of ~35 or so

I must be missing something because when I read the posts made by Richard I couldn’t find this claim. Can you please quote Richard in context where he makes this claim?

Thanks
Andrew

[Richard Nisley]

The old saying, “horses for courses”, has applicability for windshirts.

If you are an aerobic athlete who can UL backpack at an average 7 METS all day (highest possible sustainable MET rate), then ~35 CFM is the optimal windshirt moisture transport / windblocking cross-over point. The pre-2013 Houdini is an example of this design. On the downside, most of this class have a HH less than 100 mm H2O.

If you are are not an aerobic athlete, you will probably be quite happy with a windshirt fabric like Ventum. I tested its CFM at 6.6 combined with a HH at 281mm H2O (exceptional). Consider that eVent fabric only passes about 1/10 the CFM and sweat vapor transport. Also consider that Ventum passes twice the CFM and sweat vapor transport as the 2013 and later Houdini with a similar high HH.

I formally reviewed Ventum about a year ago Here

[James holden]

If your MET level AND/or environmental factors are varying such that you are sometimes comfortable, sometimes cool, and sometimes warm then a base layer and approximately 35 CFM windshirt is required for optimal comfort. This scenario occurs as you quickly move through varying micro-climates and/or your MET rate varies with the terrain.

also more on it at …

If due to changing micro-climates and/or a varying MET rate, you are SOMETIMES COMFORTABLE, sometimes too cool, and sometimes too warm, wearing mid-point comfort insulation, then an optimal CFM wind shirt is without equal. The wind shirt adds about .6 clo of non-wind-speed-varying insulation to offset sometimes being too cool. When you are sometimes too warm, your body will automatically generate sweat to reduce your temperature through the latent heat of evaporation. The optimal CFM wind shirt allows that evaporated sweat to automatically and quickly cool you to your body’s optimal comfort level. It does this without leaving sweat on your skin. Non evaporated sweat on ~20% of your skin surface is perceived as being uncomfortable. It is primarily the sweat caused friction between your skin and your base layer that causes the discomfort.

All wind shirts are a compromise between providing warmth and facilitating your body’s automatic cooling when needed for comfort. There are a large number of light weight wind shirts available with CFM values less than 10. If you want something to wear for low MET activities, they are great choices.

Backpacking is an activity that averages 7 MET; that is the highest indefinitely sustainable MET rate. The sometimes too warm case, mentioned above, creates a unique engineering problem. That is, “wearing a base layer and a shell layer, what is the cross-over point for the maximum moisture transport curve and the wind resistance curve?” The engineering solution is a unique compromise.

https://backpackinglight.com/forums/topic/100458/page/2/#comments

An optimal windshirt design has a CFM of about 42.5 at the crossover point for the maximum water vapor transport and the minimum wind blocking. Woven summer shirts typically have a CFM in the 48 – 88 CFM range. Fleece has a CFM average of about 240. To never impede physical performance you need something like a loose weave T-shirt at ~400 CFM.

My WILD GUESS is he is describing something in the 88 CFM range (near maximum air permeability for a woven fabric). A single coffee filter is about 70 CFM and a doubled filter is about 35 CFM. Somebody needs to blow some hot air through both and report back how they compare.

https://backpackinglight.com/forums/topic/102981/

I measured the older Pertex Classic fabric and it was 3 CFM. Assuming this is the Pertex fabric used in your windshirt, it is a very poor choice for use while UL backpacking. I also measured the North Face Verto windshirt using the newest Pertex GL fabric and it was even worse at .53 CFM, the same as the Thru Hiker eVent. I then had a forum member, who purchases a lot of Pertex fabric, contact his rep. The rep’s spec for the fabric was less than 1.97 CFM.

At a 7 MET exertion level (UL backpacking average), in average summer mountain temperatures and wind conditions, most people find the Houdini air permeability the optimal windshirt available. I measured the spring 2012 version of this windshirt at 35.8 CFM. The reason its air permeability is optimal is that this is the level of air permeability that will JUST PASS the AVERAGE EVAPORATED SWEAT moisture while UL backpacking. More air permeability than provided by the Houdini is not a wise choice for most people.

https://backpackinglight.com/forums/topic/70722/

UL backpacking is the only common sport that produces 7 MET activity and its attendant heat on a sustainable basis. It is the case in which most windshirt manufactures don’t specifically target. Those that do, size the windshirt to create an optimal gap between it and the base layer of 3/8″ – 1/2″ adds .6 clo of warmth for free. They provide a weave that passes approximately 35 CFM because this the level that provides the most exports of body moisture with the least vulnerability to forced convection heat loss. Those windshirts optimize for UL backpacking also have either an EPIC thread coating for garment life time DWR or a fluorocarbon coating for moderate life DWR.

A windshirt designed for UL backpacking will best maintain a thermal neutral body temperature without requiring the wearer to constantly diddle with it. It will also yield a HH value in the range of .43 – .75 PSI (300 – 527 mm H2O HH).

In summary, a properly designed windshirt for UL backpacking adds warmth by the addition of .6 clo in the base-layer-to-windshirt air gap plus another .6 clo from the windshirt’s boundary layer (this will vary with wind speed). When your body goes above its thermo-neutral point, you start producing sensible perspiration. If the air permeability allows the moisture to evaporate and pass through to the outside environment, the latent heat of evaporation cools your body back to the thermo-neutral point. If the air permeability is not sufficient to pass the amount of moisture being produced to the outside environment, the water stays on your body. Once approximately 20% of your body is wet, you have a feeling of discomfort. This is primarily sensed by the increased clothing friction. To put the difference in ability to pass moisture out in perspective, a Frog Togg or equivalent garment will pass .17 CFM and a pre-2013 Houdini will pass 35 CFM. Hence, a dramatic difference in the ability to automatically cool your body as required by different brief micro climates without any diddling.

https://backpackinglight.com/forums/topic/87001/page/2/#comments

im sure theres more links we can dig up
now im not saying this is “ideal” for everyone, especially if folks run cold

but in john’s “wind jacket part 2” article, a quick read basically implies that lower CFM windshirts are the best, and the article reads like richards data supports that conclusion … which im pretty sure it doesnt

and in the “reviews” state clearly if the gear was purchased or provided by a sponsor and that one is sponsored by em

;)

[Justin Baker]

While we are on the subject of windshirts, are there any out there with a similar fit and fabric feel to the black diamond alpine start with about a 35 cfm? I find the start isn’t wind resistant enough in some situations. I tried the squamish but the fit was all wrong for me, way too boxy.

[Andrew Priest]

Thanks Eric. I see all your quotes/links are not to the source you claimed initially hence my question.

[Richard Nisley]

Justin,

Regarding options for a combination of light aerobic fabric / good HH / specific cut, one of your options is having Luke’s UL make it in his Argon 2RS. Ken Larson, and possibly others, have posted reviews on this windshirt to the forum.

I tested his windshirt material on 5/15/15 at .90 oz/yd2, .045mm thick, 40.13 CFM, and 351.50mm H2O.

[Author]

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