Sock Fibers and Moisture Management - Cotton vs Wool vs CoolMax [Blister Prevention Office Hours]

Blister Prevention Office Hours 😓Sock Fibers and Moisture Management - Cotton vs Wool vs CoolMax 😓
➡ A monthly Q&A hosted by podiatrist Rebecca Rushton (the BlisterPod) for Podiatrists, Physios, Athletic Trainers, Wilderness Medics, Race Medics and Event Directors, Educators, Footwear Designers, Footwear Retailers, and anyone who deals with foot blisters and their prevention in a professional capacity ⬅

00:00 Premable

01:50 Sock fibers
We're going to look closely at:
- cotton, wool and CoolMax fibers
- what is moisture wicking
- does it actually happen happen in shoe
- and is it the main thing in preventing blisters

02:04 How socks prevent blisters
When we think about socks and how they prevent blisters we assume that it's the way that they deal with moisture. Moisture comes from the skin as perspiration. that is wet that. It interacts with the sock. It moves through the sock. Then it evaporates into the in-shoe environment, before hopefully moving through the shoe to the outside environment.

04:37 Fibres under the microscope
- Wool is characterized by scales. And the larger micron wools have a medulla. Finer wools like Merino do not.
- Synthetics are symmetrical and smooth.
- Cotton is a twisty "U" shape with a long narrow lumen or air space that is where the water is absorbed into the fibre.

The CoolMax sock fiber is a scalloped oval in cross-section. This fiber geometry increases the surface area by 20%.

Cotton is a hydrophilic fiber. It holds a lot of water and therefore it inhibits moisture wicking. Cotton fibers absorb three times the moisture of synthetic acrylic fibers. Once it's wet, cotton has a 10-fold greater drying time compared to synthetics.

What about bamboo? I don't know as there's nothing that I've been able to find. I would assume that it's more like cotton because we know that the drying time for bamboo is just very long - it's difficult to get bamboo socks to dry.

In terms of wool, we know that it is both hydrophilic and hydrophobic. Wool structure is round or oval and the large micron size has a medulla - an airspace in the middle of the fibre.

So, if the ability to absorb water is a favourable property of wool, you would expect to see a non-Merino wool in sock manufacture. But it's Merino we only ever hear about. Merino wool is a relatively fine Micron size, around about 19 to 21 microns. Whereas the coarse wool like around 29 microns, they have the potential to absorb more water. Air pockets in a fibre are also advantageous as air pockets aids water transportation.

11:13 MOISTURE REGAIN
This describes the ability of the sock material to attract and hold on to moisture. In terms of overall moisture regain, wool is the most hygroscopic. Cotton is the next most hygroscopic. It holds 3X that of acrylic and 14X of CoolMax.

12:31 SWELLING
The absorption of water will cause swelling of the sock fibers, this reduces air space within the sock and therefore it inhibits the movement of moisture away from the skin surface.

13:24 MOISTURE-WICKING
For moisture wicking to occur, we need that moisture gradient. Moisture is going to move from an area of high moisture to low moisture. Rossi studied the moisture storage and moisture movement properties of three common sock fiber materials.

14:19 DENSITY & CONSTRUCTION
Socks can be categorized by their their thickness and their construction technique. The density of fibers or construction of the sock can influence moisture wicking capacity. The denser the weave pattern or the thicker the padding, this may enhance moisture movement through the sock by reducing compaction and preserving that air space between the fiber networks. Please read the work of Herring and Richie back in the 1990s.

Separately, Bogerd and co-workers conducted a field study of 37 military recruits who were marching for four consecutive days in Gore-Tex lined military boots. Two socks were compared. The first sock was a blend - it was a 50% Merino wool 30% polypropylene blend. The other sock was a 99% polypropylene sock.

Looking at the construction techniques athletic sock manufacturers generally use one of two knit structures that is terry and simple jersey. It really makes a difference which way the terry loops are slanting. Just to compound the complication, when you knit a fabric, it has a front side and a back side. They look different and therefore their properties will be different.

25:08 WOOL

28:08 WRAPPING UP
Socks don't just work by reducing the COF. In fact, I would suggest that it has very little to do with with how this is achieved through moisture management. Because the kind of skin that has a low friction level is bone dry and once you've had your shoes on for a little while your feet aren't bone dry your skin isn't bone dry - it's a little bit damp and clammy.

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