It is often assumed that wool is not waterproof at all because we all remember how heavy that woolly jumper was when we take it out of the washing machine.
Yet, the truth is that wool is very water-resistant.
The reason why your woolly jumper soaks up so much water is less to do with the quality of the wool, and more to do with how old your jumper is.
Raw Wool From a Sheep
If you have ever petted a sheep, you will know its hair is wiry, tight, and a little greasy.
When sheep are caught in a rainstorm, notice how it doesn’t exactly get soaked.
The wool doesn’t look as fluffy, but mostly all the water rolls off of the sheep.
Sheep’s wool has a fatty lanolin in it that occurs naturally as the wool grows.
This means that washing freshly cut wool is tricky.
But, if you are using untreated wool, then it will retain a fair amount of its water resistance.
Sailors With Tight Sweaters
These days, sailors have a whole host of water resistant, breathable, warm materials that they can wear on ships.
However, look at old movies, and you will see sailors wearing very thick and very tightly woven wool sweaters.
This is because their tightly-woven untreated (raw) wool jumpers were very water-resistant, very warm, and very breathable so that the sailors were not soaked in sweat by the end of a shift.
New Wool and Light Woolen Clothing
Let’s say that you buy a woolen top.
It is supposed to be worn over your shirt, and it is very thin and has clearly been treated and heavily processed.
Even though most of the fatty material is gone, and even though the top is very thin, it is still fairly water resistant and still fairly warm.
Most new wool still has some of the fatty lanolin on it, which makes it water-resistant.
Plus, new wool items have fewer imperfections because they have not undergone wear and tear.
As a result, the woven material keeps out a fair amount of water.
Moist But Not Wet
Now, let’s say you have bought a wool jumper, and you have had it a few months.
Your woolly jumper is no longer water resistant.
The simple act of stretching during use, and the fact it has been washed a few times, means that the jumper is not as water-resistant as it once was.
You get caught in the rain.
You get home, and you take off the jumper.
You notice that you are slightly moist, but you are not wet.
You are not soaked to the skin because the wool will have absorbed around 20% of the water that hit you.
The fibers are able to hold about 20% of their own mass in water.
This means, like a sponge, the water was absorbed before it hit your skin.
This left you feeling moist, but not wet.
When Old Wool Fluffs Up
After repeated wearing, repeated washing, and even through improper storage, your woolen item loses its water resistant nature.
The fatty layer has been washed and worn away, the woven wool has become looser, and the fibers have started to fray slightly here and there.
Your woolen item is now happy to soak up around 20% of its own mass in water, but it is also happy to let water slip through.
If you were to try to push pressurized water through your woolen item, then it would pass through fairly easily.
If you were to drop a cutting of your woven woolen item into a puddle, then it would soak up the water very quickly.
If you were to dip a corner of your woolen item in water, and then turn it upside down, the water would pass through fairly quickly and drip out of the bottom within minutes.
In short, your older woolen items are not water resistant or waterproof.
Does Raw Wool Stay Waterproof?
Let’s say you take a few strands of raw wool that have been freshly cut from a sheep.
You drop it in water and notice it is waterproof. In other words, the inside of the fur is not affected, ergo the strands of wool themselves are technically waterproof.
If this is the case, would those strands stay waterproof?
The answer is no they would not.
The wool degrades over time, it may also rot, and is also affected by local bacteria, heat, moisture and so forth.
Strands of wool may be waterproof on their own, but they do not stay that way.
If you want to know how to waterproof wool read our article here.
The same is true when strands of wool are woven into items of clothing.
Perhaps rot is not as much of an issue because the wool has been treated, but then if you were to leave the woolen item in a festering puddle, then it would biodegrade and become far less water-resistant.
When wool is used to make things, the wool is still vulnerable to aging, environmental factors and even biological factors (like bacteria and moth larva).
Final Thoughts – Why Isn’t Untreated Wool Used for Modern Raincoats?
If old fashioned sailors were staying warm and dry using tightly-woven untreated wool, then why don’t people make raincoats out of them these days?
The answer is because untreated wool doesn’t look as nice or feel as nice.
Plus, modern weaving methods mean that wool can be woven very tightly to the point where it is mostly waterproof.
If you buy a fancy new winter coat that is made out of wool, the wool will have been heavily treated and dyed.
Also Read: Can You Dye Waterproof Fabrics
However, it will have also been woven so tightly that it still repels rainwater.
It may suffer if you leave it submerged in water for a while, but most light showers will bounce off the material.
After being caught in the rain, you will get home and notice that your coat is wet.
However, pop it on the radiator for a while, and the surface area that was wet will quickly dry off.
The water-resistance that naturally comes with new woolen items will come into play.
Plus the tightly woven fabric will also come into play so that the wool coat will keep the rain off the wearer.
This is not as effective as using a plastic mac to keep the rain off since a plastic garment will repel all the water and absorb none.
However, a woolen winter coat should be fine for most occasions because it is only going to allow water all the way through to your skin if it is subjected to heavy rain for a fairly long time.
Also Read: Is Leather Waterproof?