What Properties Influence the Air Permeability of Wind Shirt Fabrics?

I’m having trouble reconciling this:

The porosity ratio of calendered vs. uncalendered fabric is approximately 22X, and the APR ratio is approximately 158X, suggesting a positive correlation between porosity and APR.

with this:

The chart looks like it shows negative correlation between porosity and APR. What am I getting wrong?

Well, that’s because there was an error in the table – sorry about that! The APR measurements for calendered vs. uncalendered were accidentally transposed. The table has been corrected now.

This is heavy going, but interesting nonetheless! After three readings I am now understanding it…..I think.

Do you know if the Kor Airshell 2023 and Kor Airshell 2024 are constructed from the same model of Quantum Air, or are they made using a different version/model? I ask this because this is were garment manufactures (as opposed to fabric manufacturers) potentially let the end user down. In the Mountain Hardware marketing guff about these garments I’m sure (I don’t actually know) they likely just call the fabric of both the 2023 and 2024 versions “Quantum Air” so the end user would assume they are the same fabric. Obviously most users will not care, and might not even notice, but to the discerning user this is a big deal. Why the change? Cost? Improved performance? We will never know…

In my experience, another downside of crimped yarns in wind shirt fabrics is increased APR over time. I have an older Squamish that I still wear, but even after one year of use, it’s APR increased by over 100% (Mr. Seeber kindly tested it for me a while back.) I have not had other wind shirts tested like this, but I’ve owned a couple other wind shirts with crimped yarns and they also increased in permeability over time – this was quite evident by doing the Darth Vader test.

Enlightened Equipment’s fabric is an interesting demonstration of this article’s note that different calendering techniques produce different results.

Enlightened Equipment appear to use a single fabric in 7, 10, and 20D weights. It looks calendered (shiny) and they use it for most of their products, including down. The fabric tested in their Copperfield windshirt is only moderately air permeable (4.7 cfm for 10D and 7 cfm for 7D), which also is consistent with calendering.

However, the measured MVTR was very high: 3520 g/m2/24hrs for 10D and 3760 for 7D. This is a clear outlier from the trend that MVTR often (but not always) correlates with air permeability as Stephen Seeber discussed in one of his articles.

In contrast, HyperD 1.0 osy (20D) tested at an impressive 3813 MVTR and 38 CFM when uncalendered, while the calendered version of the same fabric tested at a rather low 1368 MVTR and <1 CFM.

TLDR: There is a huge change in HyperD’s MVTR and CFM when calendered, while EE’s apparently-calendered fabric retains very high MVTR.