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The Benefits of Merino Wool – Part 2, Structure

Last week, we discussed how merino wool’s relationship with water lends it several benefits: merino keeps you both warm and cool, wicks moisture, resists water-based stains, is antibacterial and anti-odor, is fire and static resistant, helps you sleep, and benefits your skin. As if this weren’t enough, wool has a second magic power – its physical structure – that adds to its long list of abilities. This week, I’ll explain how merino wool’s physical structure results in a fiber (and fabric) that is super-soft and elastic, but also resilient and strong.



Remember that a merino wool fiber has many layers. In a way, merino is a bit like a shallot – peel off the crispy brown outer layer, and you’ll discover two or three mini purple shallots stuck together whereas before, it looked like you had just one large shallot. Separate these mini shallots, and you’ll see each one has its own layers like an onion.

Merino wool fibers work a similar way. From the outside, a merino fiber looks like just one solid scaly fiber (or one brown shallot). Peel off its outer layer (the cuticular scales and cuticle layers), and inside there’s a yin-yang like structure, with half made of para-corticle cells and the other half made of ortho-cortical cells. Look closely, and you’ll see that each of these cells is like a tiny shallot. Take one of these shallots (aka cells) and peel off its first layer – the cell membrane complex – to reveal all the macrofibrils inside. Each macrofibril is again like a microscopic shallot, with more layers. Take this microscopic shallot, peel off its outer layer – the matrix – to reveal the microfibrils (more micro-micro shallots). One more time, peel off the outer layer (protofibril) of the microfibril (micro-micro shallot) to finally get to the twisted molecular chains and helical coils, the smallest part of the merino wool fiber.



So how does this complicated structure make merino wool both elastic and strong? For merino’s elasticity, we can look towards its inner most helical coils. These coils act just like a spring or rubber band – they can easily stretch without breaking and snap back into place without damage. These coils are made of proteins like keratin, which (keratin in particular) provide further strength and resilience with their strong but flexible scaffold-like structures.

Though these twisted molecular chains and coils are strong on their own, they become even stronger when twisted all together and encased by the protofibril, thus becoming microfibrils. Icebreaker says it well –

“The microfibrils in the matrix are rather like the steel rods embedded in reinforced concrete to give strength and flexibility.”

When you look at a merino fiber, therefore, imagine it as a skyscraper made of elongated shallots-within-shallots. Just as real skyscrapers can withstand hurricanes and earthquakes, merino too gains its strength and flexibility from its innermost structures. This allows merino to bend up to 20,000 times with out breaking, and can stretch more than 30% of its length and still return to its original shape. 

If a material can be this strong and flexible, how is it that it can also be super-soft? After all, wool does have a reputation for being scratchy. And it is true – broad wool (fibers from sheep that are raised for both their meat and wool) is scratchy. But, there are different classifications of wool, which are defined by the diameter of the fiber in microns (one millionth of a meter). Broad wool is one type (greater than 25 microns), followed by medium (20.6-24.5 microns) and then fine wools (less than 20.5 microns). Merino wool falls with the fine to medium wool classification, with most merinos being fine. In comparison, the average human hair is thick and chunky with a diameter of 50-100 microns.



So what does this mean for softness? Softness is generally measured by the diameter of the fiber – the finer the fiber, the softer. Moreover, back in 2017, a group of researchers found that wool fibers over 30 microns are perceived as itchy, though not a source of allergens themselves. The itchiness of the thicker wool fibers is because these coarser fibers are just big enough to literally poke your skin – it’s like a million microscopic pricks all over from the fibers sticking out of the fabric. Merino is different. It’s fibers are fine enough that they don’t trigger an itchy response from your skin. And furthermore, because they are so flexible, merino fibers actually curl up against themselves when pressed against your skin – meaning no sharp pin pricks.


image by Woolmark


Thus, merino wool is super soft, strong but flexible, temperature regulating, and fire and static resistant. Perhaps its most amazing ability is that it can do all of the above, completely naturally and sustainably. We’ll discuss just that in Part 3 – Sustainability!