There is however another side to all this, and it's the reason why many people think that wool retains its insulation when wet, even though it does not. The faster drying time of synthetic insulation (in many cases much faster), creates a feeling of coolness against the skin. The fabric dries by letting the water evaporate faster. The evaporation process creates cooling. That is why we often feel a chill after getting wet in synthetic clothing. The insulation loss from getting wet is about the same, but the faster drying material feels cooler while drying. Wool spreads out that chill over a longer drying period, so it is less noticeable, even though it persists for a longer period of time. The overall amount of cooling from evaporation is the same, it is just that it is concentrated in a shorter period of time with synthetic insulation, so we feel it more.
At least that's my understanding.
Wood Trekker, first off, great tests. Thanks for taking the time to actually create an experiment and gather real data. You make a very good point here. Rate of cooling has a very real impact on the wearer. In hot weather, rapid cooling is beneficial to help cool our bodies when over-heating is the greatest risk. In cold weather (the traditional domain of wool) rapid cooling can be miserable and even dangerous. A slower rate of evaporation allows our bodies to retain more heat and doesn't unnecessarily lower our temperature. Wet clothing itself isn't dangerous, it's cold wet clothing.
Part of the problem some people are having understanding the usefulness of Wood Trekker's test is that he compared thick wool knit toques to a 200 weight fleece. These are insulative layers, not base layers. And 200 weight fleece is a totally different kind of synthetic than most synthetic base layers. It simply doesn't absorb much water. No one wears fleece base layers as you would end up a gross, sweaty, drippy mess. Also, his tests compared completely saturated materials, simulating a dunking in a stream or something like that, not sweat generated by hiking which is much less volume. His tests are useful for analyzing wool insulation in a scenario where you've gotten completely soaked and can't get dry easily. Read his comments after the fleece test to see that Wood Trekker isn't claiming this proves synthetics beat wool.
Another aspect that the testing doesn't really measure is evaporative cooling, since it is only 30 minutes long. There is a slight hint that soaked wool is beating soaked 200 weight fleece past 30 minutes, which would be in keeping with Wood Trekker's comments. (Besides the old saying "wet wool insulates" is based on wool vs. cotton, not wool vs. fleece)
Wood Trekker, what was the weight of the water absorbed by the fleece? The wetted wool absorbed over twice it's own weight in water, and I doubt the fleece would have even doubled in weight. If a dunking is in your future, I would heartily recommend synthetic layers. Possibly a good lesson for rainy days/high humidity conditions?
For my two cents, synthetic base layers are simply uneconomic. They can be a bit cheaper up front (unless you're buying Patagonia Capilene), but I have to throw them out after each season because the smell becomes offensive to me (I have a moderately sensitive nose due to chemotherapy). I don't believe merino is scent-free, it eventually smells too, but it doesn't smell like some unbathed hobo last wore it when it is fresh out of the dryer like my synthetics all do. A little wet dog smell with new merino is tolerable to me.
Obviously all fabrics provide benefits and drawbacks. I love my synthetic boxer briefs for the lack of chafing and quick drying. I love my synthetic fabric pants for durability, water repellency and quick drying after hiking through damp grass and brush. I love my merino base layers in the fall for lack of stink and good balance between wicking and insulation. I also pack an extra merino shirt to change out of after hiking up the hills in the pre-dawn hours. This system works for me, and each hunter should figure out which combination of fabrics works for their bodies, their conditions, and their hunting styles.
Thanks again Wood Trekker for actually gathering some real data.