Wool and Water
HA-HA ... SOAPBOX ALERT! ...
Wool handles water much better than other fibers.
Nature has astonishingly sophisticated tools with which to implement exquisite designs that are tested ruthlessly, remorselessly and incessantly.
Please note there are related pages:
Wool enables sheep to comfortably withstand a very wide variety of weather conditions and maintain a body temp of about 102F (39C), just a little warmer than us, with minimal expenditure of energy. At WeatherWool, we thankfully use Nature's gifts ... and stay out of the way.
This discussion can get pretty long and involved, that's why we use 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. (And here's something that's really crazy ... when I search for info on wool, I often find this website listed as a source!) 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 page doesn't really have much in the way of stories/examples ... it's more about the wool itself. We have separate pages where we relate some real-life stories about WeatherWool in the RAIN and WeatherWool for trekking.
BUT ... stories are memorable, so here's a story. In my early teen years, we loved to play (American-style) tackle football in horrendous weather ... cold, rainy, windy, muddy ... we got horribly filthy, and I can hardly believe that our Moms put up with it! But anyway, I had an old wool jacket that was scratchy and not comfortable, but it was my football jacket and it always impressed me how that jacket worked better and better through the course of each cold, wet, muddy football afternoon.
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 in the following diagram:
(The diagram above has been reproduced in slightly different form by a lot of people and I don't know who to credit for it. If anyone has info, please let us know! Near as I can tell, it's a modification of a diagram from Australia's Commonwealth Scientific and Industrial Research Organisation, and as a government-sponsored agency I believe it's OK to use their material.)
Below is another version of the same diagram. The parts of the fiber are easier to see, and there is a sizing ruler added. A nanometer (nm) is a billionth of a meter.
The outermost layer of the wool fiber, the epicuticle, repels water. (The lanolin in wool also helps repel water.) So when you are out in the rain, even extended rain, or immersed in a river or the surf for a shorter time, the wool gets wet on the surface, like human hair would, but does not soak up any water. (This behavior is completely different than typical cotton, which immediately fills up with all the water it can hold.)
BUT ... here is where wool's complex structure comes into play ... the interior of a wool fiber attracts water. The surface of the epicuticle is scaly, and water molecules, particularly in the form of vapor, can slip through the spaces between the scales. Once inside the fiber, water molecules adsorb -- form hydrogen bonds -- to amino acids at the surface of internal structures. Creating 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!
Everyone has seen how water tends to stick together ... rain running down a window tends to form pathways that concentrate the flow. Wool takes advantage of this tendency by shedding liquid water at the epicuticle, but admitting water vapor between the scales of the epicuticle.
During a rainy hike, a wool garment will shed the rain (liquid water), but adsorb internally the water vapor coming generated by the body in response to the effort of hiking. Many times I've hiked in warm, heavy rain, wearing only a ShirtJac on my torso, and been amazed and delighted that I didn't get wet with sweat or rain.
This complex behavior is not useful only in rain. Wool clothing creates a great microclimate within which a human can be remarkably comfortable. On a wet day, after the rain, or just during high humidity, wool will adsorb humidity from the air, preventing it from reaching you, and keeping a relatively dry microclimate around the person wearing it. And it works the other way, too ... if you are working hard enough to perspire, the wool can adsorb the water vapor coming off your body, preventing the vapor from condensing on your skin ... and so you don't have the impression of sweating. What's more, wool can do both these things at the same time ... such as during a rainy hike ... protecting you against moisture coming in, but also adsorbing the moisture produced by the body. And because the water is inside the woolen fiber, the outside of the fiber feels dry ... because it IS DRY.
What's also really great is that this behavior helps keep people warm in winter but also helps keep people cool in the heat.
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 increase in water vapor before it condenses on the skin creating wetness ... wool captures and holds 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. Fleece won't actually absorb the water, but it will be wet and hold the water against you, where it will rob you of heat
- Cotton and other plant material absorbs all the water it can ... immediately ... death trap
- Wool adsorbs a lot of water ... slowly, and internally ... you may feel the weight, but you don't feel the water
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.
Advisor Mike Dean tells me this is a critical factor, and when he was field-testing his first piece of WeatherWool, he chopped a hole in the ice of a lake to see how long it would take to sink the AAJ. He got tired of waiting and held the jacket underwater with a stick ... and then put it on ...
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.
OK ... I love stories, so here is another story. A tester for the United States Army has tested our Anorak extremely thoroughly ... that is, i sent him one for eval, and he's been wearing it an awful lot for over a year as of March 2020. But his professional evaluation was that the Anorak is not suitable for regular Army because, he told me, the warmth to weight ratio is inferior to modern synthetic materials. And my response was ... "under what conditions?" ... People making these comparisons always seem to focus on dry conditions, when it is much easier to stay warm. What's the warmth to weight ratio after you climb out of a river, or even after a period of strenuous exercise?
We have a related page, The Science of Wool, that has some of this same information, plus quite a bit more.
27 March 2020