Wool, Hair, and Kemp: What’s in a Fleece?

Known for her expertise in sheep breeds and fleece, Deborah Robson puts individual wool fibers under the microscope.

Deborah Robson Jun 27, 2022 - 8 min read

Wool, Hair, and Kemp: What’s in a Fleece? Primary Image

These Romeldale samples exhibit the classic properties of wool and no hair. Photos by George Boe

In this excerpt from “Wooltripping: What’s Inside the Not-So-Familiar Wool Fiber?” from Spin Off Spring 2018, discover the differences between wool, hair, and kemp—and why each one has its place.

Three distinct types of fibers can be found in fleeces: wool, hair, and kemp. A wool-growing sheep’s fleece can contain wool alone; wool plus hair; or wool plus hair plus hair plus kemp. (Occasionally you’ll find one that is mostly wool plus kemp, but where there is kemp, there is usually some hair as well, at least in the britch, or hindquarters.)

While the term wool can refer to the entirety of a fleece, it can also be used more specifically to denote the comparatively soft and relatively crimpy fiber component.

In Merino, the fleece is all wool. In a breed like the North Ronaldsay, the undercoat is wool and the outercoat is hair. Hair fibers are variously called hair, heterotype, or (less commonly) gare fibers, and they tend to be sleeker, straighter, and less crimpy than the wool fibers. It can be difficult to draw a firm line between hair and wool, especially when there are a lot of intermediate fibers in a fleece. In some cases, the single fiber’s growth will be wool-like in one season and hair-like in another.


To teach yourself the essential differences between wool and hair, take a look at a double-coated fleece. Its staple or lock will be triangular, and the hairs will be longer than the wool undercoat. Compare this to a fine or medium-wool single-coated fleece as well as to a longwool fleece—none of which have hair components. Once you have the basics, you will be better equipped to navigate the intermediate manifestations.

SOSP18 1086 resA double-coated fleece such as Navajo Churro includes longer hairs and shorter wool undercoat.

By definition, in kemp fibers the medulla takes up more than 60 percent of the fiber diameter. Kemps tend to be short and brittle and thick (high fiber diameter).

They are most often white, although they can also be black or red. Because of their stiffness, kemp fibers are itchy. For most breeds’ fleeces, they are undesirable; however, in tweed fabrics they provide characteristic, even essential, texture and color flecks. It’s often said that kemp fibers don’t take dye; they do, but because of the fiber structure, the dye is drawn inside and is likely to be unseen or only partially visible.

Interested in learning more about the structure of wool? Check out the full article in the Spring 2018 issue of Spin Off.

Also, remember that if you are an active subscriber to Spin Off magazine, you have unlimited access to previous issues, including Spring 2018. See our help center for the step-by-step process on how to access them.


  • American Sheep Industry Association. Sheep Production Handbook. Englewood, Colorado: American Sheep Industry Association, 2015.

  • Berry, Mary. “Prinsesstårta.” The Great British Bake Off. BBC. (accessed August 24, 2017).

  • Caldwell, Jonathan P., David N. Mastronarde, Joy L. Woods, and Warren G. Bryson. “The Three-Dimensional Arrangement of Intermediate Filaments in Romney Wool Cortical Cells.” In Journal of Structural Biology 151, no. 3 (2005), 298–305.

  • Cole, Joanna, and Bruce Degen. The Magic School Bus Inside a Beehive. New York: Scholastic, 1996.

  • ———. The Magic School Bus and the Climate Challenge. New York: Scholastic, 2010.

  • Harland, Duane P., Jonathan P. Caldwell, Joy L. Woods, Richard J. Walls, and Warren G. Bryson. “Arrangement of Trichokeratin Intermediate Filaments and Matrix in the Cortex of Merino Wool.” In Journal of Structural Biology 173, no. 1 (2011), 29–37.

  • Hearle, J. W. S. “An Introduction to Protein Fibres.” In Handbook of Textile Fibre Structure: Natural, Regenerated, Inorganic and Specialist Fibres, edited by S. Eichhorn, J. W. S. Hearle, M. Jaffe, and T. Kikutani, 95–107. Boca Raton, Florida: CRC; Cambridge, England: Woodhead, 2009.

  • Hearle, J. W. S. “The Wool Fibre.” In Wool: Science and Technology, edited by W. S. Simpson and G. H. Crawshaw, 80–129. Boca Raton, Florida: CRC; Cambridge England: Woodhead, 2002.

  • Höcker, H. “Fibre Morphology.” In Wool: Science and Technology, edited by W. S. Simpson and G. H. Crawshaw, 60–79. Boca Raton, Florida: CRC; Cambridge, England: Woodhead, 2002.

  • McFadden, William D. Wool Science. Boulder, Colorado: Pruett, 1967.

  • Millington, K. R., and John A. Rippon. “Wool as a High-Performance Fiber.” In Structure and Properties of High-Performance Fibers, edited by Gajanan Bhat, 367–408. Cambridge, Massachusetts: Woodhead, 2017.

  • Plowman, Jeffrey E., Louise N. Paton, and Warren G. Bryson. “The Differential Expression of Proteins in the Cortical Cells of Wool and Hair Fibres.” In Experimental Dermatology 16, no. 9 (2007), 707–714.

  • Popescu, Crisan, and Hartwig Höcker. “Hair: The Most Sophisticated Biological Composite Material.” In Chemical Society Reviews 36, no. 8 (2007), 1282–1291.

  • Ramanathan, N., J. Sikorski, and H. J. Woods. “Electron Microscope Studies of the Surface Structure of Wool and Other Fibres.” In Biochimica et Biophysica Acta 18 (1955), 323–340.

  • Rippon, John A. “The Structure of Wool.” In The Coloration of Wool and Other Keratin Fibres, edited by D. M. Lewis and John A. Rippon, 1–51. Oxford, United Kingdom: John Wiley & Sons, 2013.

  • Rogers, George E.“Biology of the Wool Follicle: An Excursion into a Unique Tissue Interaction System Waiting to be Re-discovered.” In Experimental Dermatology 15, no. 12 (2006), 931–949.

  • Rogers, George E. “Electron Microscopy of Wool.” In Journal of Ultrastructure Research 2, no. 3 (1959), 309–330.

  • Rogers, George E. “Hair Follicle Differentiation and Regulation.” In International Journal of Developmental Biology 48, no. 2–3 (2004), 163–170.

  • Ryder, Michael L. “Fleece Grading and Wool Sorting: The Historical Perspective.” In Textile History 26, no. 1 (1995), 3–22.

  • Woods, J. L., and D. F. G. Orwin. “The Cytology of Cuticle Scale Pattern Formation in the Wool Follicle.” In Journal of Ultrastructure Research 80, no. 2 (1982), 230–242.

  • Wortmann, Franz-Josef. “The Structure and Properties of Wool and Hair Fibres.” In Handbook of Textile Fibre Structure: Natural, Regenerated, Inorganic and Specialist Fibres, edited by S. Eichhorn, J. W. S. Hearle, M. Jaffe, and T. Kikutani, 108–145. Boca Raton, Florida: CRC; Cambridge, England: Woodhead, 2009.

Deborah Robson keeps diving deeper into the world of natural fibers, especially the magical ones grown by animals. For more of her work, see Handspinning Rare Wools, The Fleece and Fiber Sourcebook, The Field Guide to Fleece, and her website at

Originally published February 28, 2018; updated June 27, 2022.