Wool and Water
The way wool interacts with water is a huge advantage over other fibers. This discussion can get pretty long and involved, so we decided to create a separate page. Also, I cannot claim that I really understand all of it. I've read a lot of material on this subject, and much of it I've read more than once. But what I can say for sure is that I've worn wool in a lot of conditions, some of them quite strange, and been very impressed with the results.
This is me, dressed in wool ... and barefoot ... fishing in steady, light rain, strong wind (15 knots / 28 kph) and cool temps ... both air and water at 55F/13C. The surf was surging up to my thighs, and splashing above my waist, so chest waders would have been the normal choice, but they can be extremely dangerous ... and anyway, I always like to see what the wool can do. MidWeight Pants and FullWeight ShirtJac were fine in the surf and fine in the restaurant afterward.
But exactly how does wool handle water so well? Here is what I've been able to pick up from the sources.
The structure of wool is very complex, and different parts of the wool fiber have different properties, as shown here:
The outermost layer of the wool fiber, the cuticle, repels water. So when you are out in the rain, or in a river or the surf for a little while, the wool gets wet on the surface, like human hair would, but does not soak up any water. BUT ... here is where wool's complex structure comes into play ... the interior of a wool fiber attracts water. The surface of the fiber is scaly, and water molecules can slip through the spaces between the scales, where it forms hydrogen bonds with the amino acids inside the fiber. Creating these hydrogen bonds actually releases heat (called the heat of sorption)! This is a pretty big deal for someone stuck outdoors in a humid cold. I think this behavior explains why wool is so popular on America's Gulf Coast ... it doesn't get all that cold there, but the humidity is crazy. I was in Mississippi once with the thermometer showing right around the freezing point, but it seemed MUCH colder because the humidity was so high .... and I come from New Jersey, where I thought we had humid cold! Wool clothing creates a great microclimate for a human to be comfortable in.
Of course, over time, the water adsorbed internally by the wool will dry out. I've gotten my wool plenty wet but hanging it overnight in a warm dry room is all it takes to get the moisture out. But it does dry slowly, in part because, while you are wearing the wool, the drying process costs heat, and Nature doesn't want a sheep using a lot of body heat to dry itself.
In less abstract terms:
- Our friends in Mississippi feel wool's benefits as soon as they step out from their warm, dry homes into that bone-chilling Gulf Coast chill. When the warm, dry wool is suddenly moved to cool/cold and humid air, the wool will immediately begin to adsorb water internally, and produce heat while at the same time keeping the humidity from reaching the wearer. The wool buffers the humidity, adsorbs the moisture and creates a comfortable microclimate.
- When someone wearing wool suddenly starts working hard and creating sweat vapor, wool can adsorb the sudden increase in moisture before it condenses on the skin creating wetness, and capture and hold the heat contained within the vapor. Later, both the vapor and the heat will be slowly released. Feeling sweaty or clammy can be avoided. Also, again because wool will adsorb the vapor of perspiration, the wearer is cooled more quickly and kept more comfortable than if another fabric had been worn.
- I have even seen claims that wool, compared to polypropylene, the most common synthetic, enhances athletic performance because wool allows the athlete to dissipate more heat, thereby avoiding exhaustion.When someone wearing wool experiences a sudden increase in humidity, wool can handle that as well, buffering the moisture and keeping the wearer comfortable.
One thing I read pretty often is that other fabrics dry quicker than wool. I'd say this is only half-true, because different materials get wet differently, strange as that may sound.
- Synthetics absorb very little water
- Cotton absorbs all the water it can ... immediately
- Water adsorbs a lot of water ... slowly, and internally
The picture above was taken during a test in a pool. I laid out my old All-Around Jacket (same one that went in the river) on top of the water. At the same time, I laid out a cotton T-Shirt. The cotton shirt sank in seconds. The All-Around Jacket began to get wet very, very slowly, and it took 65 minutes to sink.
Wool can adsorb (internally) a LOT of moisture. And it takes a long time to release that moisture. BUT ... the outside of the wool, the part of the wool we touch, dries off really quickly, and it feels dry because it IS dry. Synthetic materials will hardly soak up any water at all, and so they do dry off quickly. Cotton will immediately absorb all the water it can hold, and it will dry more quickly than wool, but cotton will feel damp, and will pull huge heat from you, until it is completely dry. The "wetting" behaviors of wool, cotton and synthetics are completely different, so it is hard to compare them on an "apples to apples" basis.
2 June 2018