In reply to Sharp:
> I have to disagree with you there, synthetic fabric is made of a solid non permeable, hydrophobic plastic fibre and wool is like all wool, made of natural hairs with hydrophilic cores and scaley surfaces. In terms of structure you can't really get much different.
Note that I was discussing
fabrics, not the individual
fibres from which yarn is made, and then used to make a fabric.
The problem I have is that people say 'merino is slow drying', when, what they generally mean is 'a thicker garment takes longer to dry'. I don't think it's a fundamental property of the wool fibre, but rather of the entire fabric assembly.
Now, call me a sad gear geek, but I have done tests where I weighed three similar design, but different fabric base layers into a rinse & spin cycle, weighed them when they came out, and then set them to dry, weighing them at regular intervals. I recall that I found that all three fabrics gave similar amounts of retained water following the spin, as a percentage of the garment mass, and there was little difference in the slope of the drying curves, again expressed as retained water as a percentage of dry garment mass. Sadly, I can't seem to find the data, and my memory may be defective. I might have a go at repeating the experiment tonight; the initial, post-spin water mass will be interesting, given the oft-stated '30% water absorption into the wool fibre'. However, in the mean time, this paper might make interesting reading:
http://nopr.niscair.res.in/bitstream/123456789/6881/1/IJFTR%2034%284%29%203...
It seems they did pretty similar test to those I did, only using specially-constructed fabrics of similar weights and thicknesses, and different fibre mixes. The drying times are quite interesting, especially those of a wool/synthetic blend, which gave a drying time longer than either of the consituent fibres... Their wicking results are no surprise: wool is pretty poor.
Water absorbed into the fibre core (as opposed to stored mechanically in the yarn fibre bundle and the knit/weave structure) will take a long time to evaporate off. This means that the cooling effect of this residual water is low; once the mechanically-stored water has evaporated, the main cooling power of the fabric is gone, just like for a synthetic. Of course, the faster a garment dries (assuming a similar water load), the larger the cooling power, so the faster drying will chill you; thus you get a shorter, more intense thermal shock from a faster-drying garment, compared to the longer duration, but less intense thermal shock from a slower-drying garment. Both of these situations can be considered beneficial, and detrimental, depending on the application...
As you rightly say, to get similar absolute drying times from a merino garment and a synthetic garment, they need to be the same weight, and it's easier to make a thin, robust synthetic than it is to make a thin, robust merino base layer. I commented that the downside of merino is the fragility.