Measuring the Fineness of Cotton
I received a question from Linda Holt, an astute cotton spinner, who noticed a subtle difference between two types of cotton she was working with. She wrote:
"I was recently spinning some Sea Island Cotton from Cotton Clouds and switched to Acala, also from Cotton Clouds and both listed as “Easy to Spin”! I was surprised that it took me a few minutes to make the switch! At first, I thought that the Acala cotton must have a shorter staple length. But, I tested what I had and they basically seem the same. That, of course, got me to thinking of the ‘fineness’ factor of cotton! Was cotton measured in microns, like wool?
According to Cotton Inc., "Micronaire (MIC) is a measure of the air permeability of compressed cotton fibers. It is often used as an indication of fiber fineness and maturity.” In the spinning world, however, I’ve never seen cotton listed with a micron (or, micronaire) count like you would wool! Just curious to know if I’ve missed something or is the difference so small it’s insignificant? Yet. . .I did notice a difference! In fact, the Acala reminds me of bunny fur!!"
Yes, Linda, they do measure the micronaire of cotton. Each bale has two samples taken from the bale and sent to classification stations. There are 12 around the USA to measure and evaluate each bale of cotton.
However, as spinners we have never been concerned enough to request what the micronaire are of the cotton. It is possible for us to request the information, but because the amount of crimp and the natural feel of the cotton is more important we have generally gone by the feel and quality of the cotton. We do know that the micronaire can be so low that commercial spinning machines are unable to spin it.
In the case you are talking about (Sea Island vs. Acala) the micronaire of the Sea Island would be much finer than that of the Acala. Also, the Acala is in the Upland family and has more crimp than that of the Sea Island, which is a longer staple fiber. Sea Island should have a more “silky” feeling than the Acala.
As more and more spinners are getting into spinning cotton, maybe we will have to become more specific about the classification of the different varieties and may ask for the micronaire of each bale.
Jill Holbrook of BrookmooreCreations, the distributor of Easy-to-Spin Cotton, kindly sent me this informative chart from Cotton Inc. to help understand the grading and fineness of cotton.
| Length of Fiber | Short Medium Long Extra Long |
Below 0.99 0.99 – 1.10 1.11 – 1.26 Above 1.26 |
Average staple length of the fiber. Measured in inches |
|---|---|---|---|
| Uniformity of Fibers | Very Low Low Average High Very High |
Below 77 77-79 80-82 83-85 Above 85 |
Measures the number of fibers with similar lengths. Too many short lengths will interfere with commercial spinning. |
| Fiber Fineness (Called Micronaire) |
Discount Base Premium Base Discount |
3.4 or lower 3.5-3.6 3.7-4.2 4.3-4.9 5 or higher |
Measures the fineness and maturity of a fiber. Measured with 2.34 gms of cotton compressed into a consistent space and air permeability. |
| Fiber Strength | Weak Intermediate Average Strong Very Strong |
23 & below 24-25 26-28 29-30 31 & above |
Strength measured by the force required to break a bundle of fibers one tex unit in size |
(Cotton Inc., 2016, Fiber properties: US fiber chart/ratings of fiber properties)