By The Numbers: What’s the Best Base Layer Fabric? Wool vs. Alpaca vs. Polyester

[Chris]

Stephen – Thanks for the follow up. Very interesting!

I wonder if there is a regular (non-mesh) shirt made of the same fabric as the Brynje wool mesh? If so, that might also be an interesting comparison to try to tease out the influence of the fabric vs. construction on the results.

[Roger Caffin]

Hi Stephen

Arcane, very arcane.

Basically, a short length (say 30 mm) of wool fibre was strung up under known tension and made to vibrate at resonance like a violin string. The frequency of vibration is proportional to the mass per unit length. The instrument details were complex.

The big problem was that the wool fibre was extremely light and air drag was significant (and organics are squooshy compared to, say, steel strings), resulting in the fibre having a resonance Q of about 10. The Q for a watch crystal might be about 10 million. It was hard to maintain resonance.

Abrupt changes in the humidity of the surrounding air flow caused the frequency to shift, by the amount of water absorbed. Ah, but what mattered to us at the time was how fast the frequency shifted: that gave the time constant for absorption into a single fibre. It was fairly short.

It turns out that this time constant hardly matters when it comes to clothing. In any loose clump of fibres there is air around each fibre, making a boundary layer, and this boundary layer dominated everything – in loose clumps. Fibres and fabric are different.

For fabric there are extra problems. The main difference between wool (or cotton) and a synthetic is that the natural fibres are hydrophilic, so the water sticks to them. The fabric stays wet. On the other hand, synthetics are hydrophobic and water does not stick. It shakes off synthetics very easily. This materially affects the drying time.

Do I still have the original data? Not a chance! That work was done in the late 70s. I am not a ‘woolie’, I am a physicist.

Cheers

[Stephen Seeber]

Hi Roger, It sounds like a fascinating (although, I expect, challenging) project.  The problem with wool research publications is that it is hard to figure out who the objective scientists are and who (they may be real scientists) are employed by the wool marketing machine.

So far, my work suggests that the characteristics of the fabric and yarns can trump the characteristics of fiber.  I am working towards repeating the work that produced the above article.  I am changing some of the methods to try to get a more nuanced read on the prior sentence.  Your description of your work seems to lend some support to this.  My last round of testing demonstrates water sticking to wool vs shaking off polypro.

In the real world, most polyester fabrics are treated to be hydrophilic, so some water will stick to the surface of the fibers but not penetrate inside.  Polyester’s performance may be somewhere in between wool and polypropylene. Or not.  In my next round, I will look at polyester that is treated to wick and polyester that is not.  I will also include some cotton, which I have never tested.  I will retest some of the merino and alpaca fabrics included in the prior study.  I expect to replace IR imaging to determine when drying is complete with a weighing method like what was used for my last posting.  The shape of the drying curves from weighing the samples provides superior insight into what is happening in the sample compared to the IR temperature data.

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