It’s the obvious question. Your clients want to know – what is the best sock for blister prevention? I’m sure you want to know. Heck, I want to know! <\/p>\n\n\n\n
Sock fibers and moisture management is something I’ve been looking at closely lately. Not just with the paper that Doug and I have recently had published<\/a>. But also in selecting our range of Injinji toesocks in the Blister Prevention shop<\/a>. <\/p>\n\n\n\n In this month’s edition of Blister Prevention Office Hours, we’re going to look closer at:<\/p>\n\n\n\n Below is an abbreviated transcript of the live Office Hours event. Please watch the video for a full replay. For references mentioned and further discussion of concepts discussed, please read our second paper in the Journal of Athletic Training 2023: https:\/\/doi.org\/10.4085\/1062-6050-0341.22<\/a><\/p>\n\n\n\n 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.<\/p>\n\n\n\n When we look closely at how moisture wicking works at preventing blisters, we are basically saying that we are implementing a coefficient of friction (COF) reduction strategy. We’re trying to keep the skin dry because we know that very dry skin has a low friction level compared to moist skin. Dry skin that provides a low COF is inferring a more slippery surface between skin and sock. Remember the whole aim of blister prevention is to, as the bones move back and forth in the within the foot, to allow the skin to move more in synch with the bone. The problem is, high friction levels (COF) that eventuate due to perspiration means the skin doesn’t move with the bone – it stays in stationary contact with the sock and shoe, resulting in larger shear deformation magnitudes.<\/p>\n\n\n\n When it comes to moisture management we instantly think of hydrophilic and hydrophobic. We all know that cotton is a hydrophilic fiber. It holds moisture. CoolMax is a hydrophobic material – it repels water. And interestingly wool is a bit of both. It’s quite the paradox, wool!<\/p>\n\n\n\n With regard to how sock fibers interact with moisture, there’s absorption and adsorption. ABsorption is the amount of water that is absorbed into the actual material. ADsorption refers to (Recommend watching the video for visual demonstration)<\/em><\/p>\n\n\n\n The CoolMax<\/strong> sock fiber is a scalloped oval in cross-section. This fiber geometry increases the surface area by 20%. So whatever way it interacts with water, it does it 20% more because there’s 20% more surface area. CoolMax fibers are hydrophobic – they repel water. So water will basically just kind of sit on the surface there and is very happy to move back and forth there’s nothing keeping it stuck to that same spot. It doesn’t know whether we want it to move to the left or to the right along its fiber. So you have to realize that the the reason it moves is presumably according to whether there’s a moisture gradient. So it’s going to move from an area of high moisture content to an area of low moisture content.<\/p>\n\n\n\n Cotton<\/strong> 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.<\/p>\n\n\n\n What about bamboo<\/strong>? 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.<\/p>\n\n\n\n In terms of wool<\/strong>, 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.<\/p>\n\n\n\n Sock fibre research focuses on several moisture-management measurements. One is moisture regain, which 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. Hygroscopic just means that the combination of absorption and adsorption. Wool holds the most moisture. So it’s interesting that we think that wool is good but cotton is bad. We’ve been told all these, years that moisture wicking is good because it doesn’t hold moisture. Cotton is bad because it holds moisture. And yet we know that wool fibre is popular and advantageous, yet it holds onto so much water, like cotton does, and yet we see cotton as a bad sock fibre. There’s a real disconnect there and I have to admit, I don’t have my head around it – I’m not sure anyone does, in terms of socks, sports and blisters. Cotton is the next most hygroscopic. It holds three times that of acrylic and 14 times that of CoolMax.<\/p>\n\n\n\n Swelling of fibres is another thing they look at. 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. So swelling is seen as a bad thing because it gets rid of all the air pockets and the air spaces can aid in moisture transport. Cotton fibers will increase volume and swell by 44 to 49 percent when immersed in water. Think back to that lumen in the the cotton fiber. It’s flat and it doesn’t take up much space. But it has the ability to fill with water and really swell that cotton fiber. Another study found that when moisture is applied, cotton fibers swell 45 percent, wool fibers 35 and acrylic 5 percent<\/p>\n\n\n\n For moisture-wicking<\/a> 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. Polypropylene showed the best capacity to wick moisture from the inside of the sock to the outside. The next best was woolen socks and the next best after that was nylon. Nylon, which is present in just about every sock to some degree, that showed minimal wicking capacity with large amounts of moisture retained on the inner side of the sock. Nylon isn’t used for moisture wicking it’s used to add stretchability and durability to the sock. But some socks have quite a lot of nylon in them.<\/p>\n\n\n\n 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 This suggested that the acrylic fibers were beneficial over the cotton fibers. The authors proposed that the results were explained by a lower friction force on the skin surface due to superior moisture management of the acrylic fibers. So that’s a reasonable thing to assume – the acrylic fibers dealt with the moisture better as it moved the moisture away from the skin keeping the skin drier and therefore more slippery such that it can move in sync with the bone at an earlier point in tim. In essence, a coefficient of friction (COF) reduction strategy.<\/p>\n\n\n\n\n
How socks prevent blisters<\/h2>\n\n\n\n
how the surface fiber reacts to the water molecules – they either hold on to it or not. Hydrophilic materials will hold that moisture on the surface of the fiber. Whereas hydrophobic fibers will just let it move easily along the fiber – it won’t hold on to it.<\/p>\n\n\n\nFibres under the microscope<\/h2>\n\n\n\n
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Moisture regain<\/h2>\n\n\n\n
Swelling<\/h2>\n\n\n\n
Moisture-wicking<\/h2>\n\n\n\n
Density and construction<\/h2>\n\n\n\n
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. So we are thinking that thicker socks are better than thin socks. The reason we think this is thanks to the work of Herring and Richie<\/a> back in the 1990s. They conducted two studies looking at blister incidence and different sock materials and construction. They took 35 long distance runners and compared blister incidence in padded socks of identical construction but different materials. The socks were either 100% cotton or 100% acrylic socks. In this study they were both thick (there’s a follow-up study where they were both thin). So in this study where they were both thick. They found there were twice as many blisters with the cotton socks and those blisters were three times the size. <\/p>\n\n\n\n