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Comfort Factor

Here is some material Advisor Bob Padula just sent me on "Comfort Factor". Holy Moly, the more I learn about wool the more I still need to learn.



Here is something [please click to read Why Sheep Don't Shrink] I wrote for the ASI [American Sheep Industry Association] 15 years ago (in 2004) regarding “comfort factor and prickle”. Things have changed since the term “comfort factor” was introduced – because the Australians started to find out how variable their wool really was.

Prior to the laserscan and OFDA [Optical Fiber Diameter Analyzer] in the 1990’s – Australian wool was sold without knowledge of how variable it was because they only used airflow to estimate the average fiber diameter of the wool. Whereas the USA ALWAYS knew how variable its wool was because we measured with projection microscope and reported the variability. Our wool grades have always included a measurement of variability, the others did not. They knew it existed, but “pulled the wool over people’s eyes” so to speak by only reporting the average fiber diameter. AND, used to claim that Australian wool was more uniform than US wool – because we freely admitted our variability – and they would not divulge or report variability.

Once the Australians started measuring with equipment that reported variability – all heck broke loose and they had to come up with fancy terms and reasons why their wool was still better – because the numbers did not show it….. it is kind of funny listening to the Australians explain stuff we’ve known about for 70 years …..

“Comfort factor” is the opposite of “prickle factor” and as you have found, based on the “30 micron” threshold. It is thought that a fiber greater than 30 micron is structurally rigid and therefore when it comes in contact with your skin, it “pokes” you rather than bending. Because prickle is negative, they came up with the inverse term of “comfort factor” – because wool has a bad image of itchy and scratchy, and people being allergic to it. This poking sensation is what causes people to think they are allergic to wool. It is a physical irritation, not a chemical one (allergy) and some areas of the body or skin are more sensitive than others. Likewise, some people have more sensitive skin (In more ways than one – Australians don’t like being wrong about wool - ) so individuals react differently. More on that later.

Research years ago found that people routinely found garments made with wool that had greater than 5% of their fibers greater than 30 micron were “uncomfortable” or itchy…… As such, garments designed to be worn next to the skin are typically made with fibers that do not have more than 5% of their fibers greater than 30 micron.

The easiest way to avoid the negatives is to use “finer wool”.

This has more to do with “next to skin wear” or base layers, than outerwear – because people will not be “commando” under their wool coats…… they wear undergarments of some kind.

All sheep will produce fibers greater than 30 micron. It is the amount or number of them that is the issue. Assuming a bell shape normal distribution – you can judge if the individual sheep will be a contributor to the problem or not. Let’s say a sheep has an Average of 20 micron and variable range of say 4 micron Standard deviation. That means that 67% of the fibers are between 16 and 24 micron. And 90% are between 12 and 28 --- guessing that the remaining 10% are either “finer” or coarser --- that leaves about 5% greater. Well, it’s not a “normal distribution” at the far ends, and there will be more fibers on the “coarser side” of the bell curve – so that 20 micron fleece is at the outer limit for having less than 5% of the fibers greater than 30 micron (Prickle)--- or 95% under 30 micron (comfort) ---- Hence the 19.5 micron limit for next to skin wear…..

A 25 micron fleece from a sheep with a Standard Deviation of say 5 micron will have 67% of its fiber measurements between 20 and 30 micron – that means that the other 33% are either finer than 20 or coarser than 30 --- so, simple math tells us that ½ of 33% is 16.5% of the fibers ---- it’s too coarse for next to skin wear.

Base layers is what brought this to people’s attention – because it is next to the skin. However, not all coarse wool garments are “itchy” – so there is also the construction and finishing that come into play.

Furthermore, the fibers on a sheep are constantly growing and never the same. The diameter of an individual fiber on a sheep varies by at least than 4 to 5 micron along the length with many times it varying by double that! When you don’t measure and report this variability – you don’t know that. One instrument, the OFDA2000 measures along the length of the fiber and reports the change in diameter every 5 millimeters. This isn’t something new about along staple variability, but advances with computers and testing made this more readily apparent. (I was doing this work 30 years ago with my sheep actually – but the hard and long way – cutting the staple and measuring with the projection microscope, then plotting the diameter differences to figure out how nutrition and management were impacting my sheep – for genetic selection programs.)

So then people were saying it is the “fiber ends” that poke the skin and cause the prickle and my wool has finer ends, so my wool isn’t the problem….. Well, not so fast.

Wool is blended to make a garment from various sources – so unless you measure all the wool the same, you can’t make those claims. And no one does that. There are “theories” out there, but no one has done the necessary research on this. They may make one test run, but they don’t repeat the test – so there are always other variables that can impact the results. But that doesn’t stop the people with wool that has certain attributes from making claims.

You are correct, with WeatherWool, we use finer wool for outerlayer garments and as a result the wool is softer feeling and not itchy/scratchy. Other woolen garments use coarser wool, even 22 micron wool should have more than 5% of the fibers greater than 30. There is more going one with construction – and that is why it is important to know the length and strength of the wool used in WeatherWool garments.

Back to baselayers --- and performance wear. When people exercise, they also increase blood flow to the skin and your skin sensitivity changes. Cold does this also. I’m seeing a trend towards using finer wool than 19.5 for base layers in active/performance wear. I’m thinking the new “prickle” or “comfort” number will be closer to say 28 or even down to 26 micron than the old 30…. We are already seeing more garments with lower micron numbers reported than 19.5.

Also, there is a difference between the raw wool micron and the resulting wool top micron…. Again, something the US has known as we have different USDA grades for raw wool and wool top…..

Hope this provides some back ground information and help.


22 April 2019