Why mix wool with rayon in technical underwear?

[Martin Nordesjö]

Long time lurker with few posts here. But now I need more technical and industry related answers than my usual channels can provide :)

Help me understand why so many brands are mixing merino wool with regenerated cellulose fibers like viscose, Tencel, lyocell, Modal or ”bamboo” (I’ll lump it together as ”rayon” for short). I just don’t understand the point of it in technical underwear. So either my knowledge about these fibers is lacking, or I’m just not appreciating the obvious benefits in this case. Or both.

I definitely appreciate the benefits of rayon in everyday use since it has the comfort of cotton but can be produced in a more sustainable way, especially if it’s Tencel/lyocell. It’s also both recyclable into new fibers and biodegradable.

However, doesn’t it also have the downsides that made us move away from cotton in outdoor clothing? It absorbs water into the fiber (it’s sponge cloth material!), the strength is low and it loses stability and shape when wet. It’s even worse than cotton in some aspects since it also loses shape when dry because of the bad elastic recovery, and it gets weaker when wet, while cotton gets stronger.

So why mix wool with it?

[Terran Terran]

Rayon is used in cooling fabrics for warmer weather.

[Iago Vazquez]

But it warmer weather it would also trap moisture against skin.

I think Martin’s evaluation of the performance of cellulose fabrics matches my experience. I would absolutely avoid it for boxers at any temperature range.

My favorite warm weather sun hoodies for the past couple of years are a bamboo blend.

[Terran Terran]

Two different yarns designed to disperse the moisture and to keep it away from the skin.

[Roger Caffin]

Wet wool is quite weak, but wet rayon keeps its strength.
The rayon in the fabric keeps the shape.

Have a look at the heels of some worn-out wool/synthetic socks. The synthetic knit is still there, while the wool has abraded away.

Cheers

[Martin Nordesjö]

Wet wool is quite weak, but wet rayon keeps its strength.
The rayon in the fabric keeps the shape.

That’s the opposite of what I know about regenerated fibers. Most types of rayon lose about half their strength when wet, and also softens. Wool also loses about 10–20 % of its strength when wet, but the fiber retains its shape better – that’s why it stil insulates instead of clinging and cooling.

Have a look at the heels of some worn-out wool/synthetic socks. The synthetic knit is still there, while the wool has abraded away.

Yes, that’s definitely true for petroleum based polymers like polyamide and polyester. I have a lot of socks and underwear with wool mixed with those fibers. But that’s not cellulose based regenerated fibers.
While they (and cotton) are stronger than wool, they are still significantly weaker than for example polyamide.

So I definitely see the point of mixing wool with a stronger fiber, but I still don’t understand the  functional reason to use rayon over polyamide or polyester in a wool blend. Or even over cotton.

[Roger Caffin]

Oops – yes, my mistake. I was thinking about nylon and PE.
I know much less about rayon, except that it is significantly cheaper. I suspect that is the reason for using it: cheaper.

Cheers

[Alan W]

Individual wool (and cotton) fibers are relatively short within long strands of yarn/thread.

With synthetics made from melts or solutions, the individual fibers can be made effectively as long as the thread/yarn itself.

This is an additional reason that the synthetic structure of a sock or other garment remains when the wool has worn or torn away.

I’ve stopped buying shirts and other wool garments that do not have say 10-15% synthetic because I got tired of darning all the little snag and wear holes in 100% merino.

As to why rayon vs. other for  the synthetic, IDK.

[Terran Terran]

Comfort.

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