What is a Micronaire in Cotton, and Why Does it Matter?

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One of the more technical terms that comes into play with cotton is the word “micronaire.” While many farmers and manufacturers are probably familiar with this measurement, the layman probably isn’t. But if you’re here—whether as a self-educating consumer or a product developer hoping to learn more about cotton—then understanding what a micronaire is will help you understand one of cotton’s most important properties.

What is a Micronaire?

Cotton Inc. defines the micronaire as follows:

Micronaire (MIC) is a measure of the air permeabilty of compressed cotton fibers. It is often used as an indication of fiber fineness and maturity.

For those that have been dealing with man-made synthethic fibers there is a way to relate. To get a ballpark value of denier (fiber diameter) can be calculated by dividing micronaire by 2.82.

But why is this important? Fiber fineness and maturity are critical for fiber processing, as well as fiber quality. Per the International Trade Centre’s Cotton Exporter’s Guide, cotton’s micronaire measurement impacts the following:

  • Processing waste
  • Neps (those knots of tangled fiber)
  • Spinning performance
  • Yarn and fabric quality
  • Dyed fabric appearance

So much like with Golidlocks’ porridge, it’s important that the micronaire measurement not be too high or too low. For yarn manufacturing it needs to be “just right.” If it’s not, you can anticipate that processing will be a hassle, or that there’s a good chance you’ll end up with uneven dye shades. The higher micronaire fiber is desired for purified cotton. It is easier to purify and forms let neps during processing (small knots of fibers). Also the larger diameter resists bending or collapse, leaving more space between the fibers for holding liquids (increased absorbency). Note that purification does not change the fiber micronaire.

What Measurement is “Just Right”?

Here’s a breakdown of micronaire readings, from most desirable to least desirable:

  • Readings of 3.7-4.2: Premium
  • Readings of 3.5-3.6 or 4.3-4.9: Base
  • Readings of 3.4-and-under or 5.0-and-higher: Discount

Most of that is cotton grown spun into yarn and micronaire values between 3.7 and 4.2 are optimum for yarn spinning, hence the premium value and the target for farmers. When the measurement comes in too low (too thin), the cotton is more susceptible to entangling around debris, which means too much of the good fiber will also be lost. When it’s too high (too thick), it also causes problems since a coarser fiber negatively affects the spinning process, as well as overall quality. It’s very difficult to spin “high-mike” cotton into fine yarn. As said above, higher micronaire is preferred for cotton purification.

What Contributes to the Count?

While most farmers are judicious in their growing, often nature has other ideas. Typically, if the growing season ends too early you can have cotton with a lower micronaire. For example, an early frost will obviously inhibit fiber development. On the other hand, higher micronaire values come from other issues like drought stress, water stress, or higher yields. In these scenarios, the plants overproduce carbohydrates, which make the fiber’s cell walls thicker. Whether we’re talking a couple of decades ago or a couple of years ago, there are challenges that cotton farmers continue to face.

The Micronaire: Now You Know

If you’re taking only one fact away from this post, it should be the following: the micronaire is a critical measurement in determining how easily cotton fiber can be processed, and is a key factor in determining potential quality. Each bale of cotton in the U.S. is tested by the USDA and the fiber micronaire is provided to the bale buyers. If you’re still itching to learn more, we’ll suggest this 2005 article from the Journal of Cotton Science. It has all of the technical data, charts, and equations you could ever ask for.

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15 Responses to What is a Micronaire in Cotton, and Why Does it Matter?

    • Hey there,

      No effect. The Mic is a product of the variety, soil type, growing conditions, amount of moisture, heat units in the soil, etc. that determines the maturity of the cotton fiber.

    • Hi Hoshang,

      Micronaire is related to fiber diameter, the higher the mic the larger the diameter. So it can be related to fineness in that respect. However it is not related to maturity.

    • Hi Tariq,

      Micronaire is the measurement of air flow resistance through a fiber sample that is compressed to a known density. It relates to fiber diameter. The finer the fiber diameter the tighter the fibers pack and thus increase the resistance to air flow. Therefore lower micronaire values represent finer diameter fibers.

      Micronaire is only used for cotton fibers and I am not aware of any way to measure it with out a micronaire instrument.

  1. please reply

    how we can improve or try to achieve mic range from 3.8 to 4.3 for farmers guidelines
    what precautions must be taken by farmers & ginners
    which variety are more preferable for mic 3.6–4.3

    • micronaire is one of the most important character of cotton variety … so you have to find out which cotton variety will produce desired micronaire in the reagion you want to produce cotton..
      there is no other way to improve or try to achive Mic range from 3.8 to 4.3.. this answer is based on general knowledge and i am not expert in this field…

      • The target range for cotton is 4-4.4 mic. All farmers chose a variety of seed that will produce the most fiber in the mic range based on the growing conditions of their region.

  2. Would like more information on:
    The correlation between the cotton mic and its influence on Dyeing ( for example dye up-take, etc ).
    Thank you.
    Much appreciated.

    • Hi Ross!

      We are glad you found our blog and reached out with your question.

      While we don’t dye fiber here at Barnhardt Cotton, we do know fibers! So, here’s what we know about the correlation between cotton micronaire (mic) and dyeing.

      Mic is related to maturity. Higher micronaire fiber is more mature and has a thicker cellulose wall. When dying, the dye is absorbed into the cellulose. As a result, there will be more dye, which yields a deeper color in fiber with higher micronaire.

      Higher micronaire fiber, however, does not spin into yarn as efficiently as mid- range mic cotton. Therefore, Cotton Mills compromise and choose fiber mic (3.8 to 4.5), which is middle ground for both dyeing and spinning.

      Hope this answers your question! Feel free to reach out to us anytime with questions about cotton or for information on our superior products!

      Director of Product Development

      • Hi Lutuf,

        The Uster or any other brand micronaire tester uses a stand weight fiber sample that is place into a cylinder. A plunger presses down on the fiber and produces a standard density fiber plug. Air flow is passed through the fiber sample and the amount of air flow allowed through is the micronaire. Larger diameter fibers will have more air space between the fiber and allow more air to flow through. Larger diameter fiber have higher air flow and which reads as high micronaire.

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