By the Numbers: The Myth of Air Permeability in Windshirts

I have been thinking that a sticky posting of my performance data for windshirts and WPB garments would be useful, especially if I could add new listings over time. If the powers that be are interested and can do that, I can provide the data.

Probably the best way is if you had an external document (like a Google Spreadsheet) that was in the first post. Then you could update the spreadsheet at will and it would be linked in the first post. I can edit the first post any time you want. How does that sound?

Edit/Clarification: That could be the first post in this thread or you could start a new thread. Whatever makes sense.

@Scott Emmens.  That is interesting, when cycling in temps around freezing my forearms get oppressively hot and clammy whilst my chest might be cold and damp.

Cycling in cold weather is weird because your core temp is high but periphery might be cold – so you can sweat into cool skin, making hypothermia a real possibility when you stop riding .

I personally find that a nylon wind garment without a membrane keeps me warmer in both cold-dry and cold-wet conditions as I sweat terribly in membrane garments.

Cycling companies, except your own excellent company, rarely make wind jackets without some kind of windstopper membrane which I think is short-sighted.

I’d only wear a WPB garment when cycling in biblical rain, a short commute or when touring as it’s really uncomfortable to ‘boil in the bag’.  A nylon top with high MVTR would be perfect for cycling IMO.  I have a quantum pro windshirt that I am trialling on the bike as winter closes in in Australia.

@Scott Emmens.

wetting out seems to be the bête noire of water resistant/waterproof garments.  I take it that MVTR is reduced markedly in the presence of liquid water on the surface of a garment?

The internet consensus is that ‘breathability ceases’ when a textile wets out but I didn’t think that it was that simple.

I’m also looking at testing grid fleece/alpha under both pertex quantum and equilibrium this winter on the bike: it’s an outstanding way to test for extreme hiking conditions!

Hi Stephen, I don’t know how the Gore RET ratings go but I just stumbled across this page:

https://www.gore-tex.com/en_au/technology/original-gore-tex-products/shakedry

and this slide which states an RET<3 – “putting it firmly in the best possible category”??:

Gore, the masters of marketing.

@Stephen Seeber.  Stephen, I am curious as to the relationship between Air permeability (CFM) and MVTR.  Intuition would suggest that a low CFM garment would correlate with low MVTR (and vice versa) but experiment (including yours) show that the relationship is not linear in tighly woven textiles even if it might be for, say, for a fishnet baselayer.

What physical prinicple allows a garment porous enough to have a moderate air permeability (such as the Houdini Air you tested) having a MVTR lower than a 0 CFM garment (such as Gore Shakedry)?

The best I could come with from reading was the hygroscopic properties of the textile itself contributing to passage of water (sorption/desorption).  I can get my head around a low CFM garment having as good a MVTR as a higher cfm garment (the analogy I thought of was that one does not die of asphyxia when taking shelter behind a rock on a windy day – blocking direct air flow does not prevent diffusion/convection) but my intuition struggles with a lower CFM garment having a relatively higher MVTR.

Intuition suggests that a high CFM garment, in still air, should still have a high MVTR as the porosity of the garment should still allow diffusion.  Obviously there are other physical properties at play than sheer pore size – is it the weave etc that also contributes here?

Thanks in advance.

Fantastic article, thanks Stephen! Do you know if the Ferrosi you tested is the current model?

REI has this to say about the Ferrosi hoodie: “Updated primary fabric is now 46% recycled with movement-mirroring stretch; body-mapped construction features CORDURA® fabric in high-abrasion zones”.

I take this to mean the fabric has changed recently.

The technical specs are listed as “86% nylon (46% recycled)/14% spandex, 90-denier stretch-woven ripstop (bluesign® approved)”.

I have some older Ferrosi pants that are listed as 86% nylon and 14% elastane (which I understand is synonymous with Spandex) so the makeup seems the same, but I’m not sure what else might have changed. I’ve seen some noticable variation in Patagonia capilene so just wondering if you’d expect differences between older and newer Ferrosi garments.

Thanks!