There's more to yarn than just yardage. Photos by Pamela K. Schultz
In 2016, I received a lovely skein of yarn for Christmas. It was a small skein of a wool, alpaca, and silk blend that seemed perfect for a hat. The hat looked great and was warm, but it had one major issue: it would constantly slip down and cover my eyes. Was there something wrong with the pattern or my knitting? No, it’s that I didn’t understand the mechanical properties of the yarn.
Mechanical properties are how a material reacts when a force is applied to it. If you pull it, does it break? If it stretches, does it go back to its original shape? If it hangs, does it drape well? If you rub it, does it pill? By understanding the mechanical properties of fibers, you can better choose the yarn for your projects and knit garments that turn out how you imagined.
There are many mechanical properties and even more fibers, so this article focuses on the ones most relevant to knitting: tenacity, elongation/elasticity, drape, and abrasion resistance, all in keratin fibers. Keratin is a protein that makes up animal fibers such as wool, alpaca, angora, and mohair. Silk is another animal fiber, but it is made of the protein fibroin, giving silk different properties.
Tenacity
Tenacity is the tensile strength of a fiber—how much force it takes to break the material in relation to its fineness. The tensile strength of a knitting yarn can vary depending on the structure of the yarn, how it was spun, and how the fiber was produced. One of the largest influences is the type of fiber.
In the world of textile fibers, keratin fibers are relatively weak, but they are strong enough for most knitting projects. You need to consider the strength required of your knitted garment. For something like a scarf, tenacity isn't very important. For a pair of socks to survive many hiking trips, the fibers making them up need to be strong. This is why wool socks often have other fibers, such as nylon, blended in to give them strength.
This sock shows signs of wear on the heel.
The tenacity of a fiber can also change depending on whether it is dry or wet. Keratin fibers become weaker in water. Tenacity in water is very important when thinking about how to launder something. Wool objects can be washed in water but should be cleaned gently. Consider how often and how intensely your knit garment will need to be cleaned when choosing your yarn. (You also need to think of felting when considering wool, but that's another topic!)
The easiest way to measure tenacity at home is to try to break the yarn apart with your hands. If it’s really easy to do, it has low tenacity. If it’s impossible, it has high tenacity. Compare your yarn to similar weight yarns in your stash to see how the different fibers change the tenacity. However, it is also important to consider other fiber properties to create your dream knit garment.
Elongation and Elasticity
Elongation and elasticity are two similar properties related to the stretchiness of a fiber. Elongation is how much a fiber can stretch before breaking. Elasticity is the ability of a fiber to return to its original length after stretching. Wool has high elongation and elasticity, meaning that it can stretch quite a lot and return to its original shape. On the other hand, angora rabbit has low elongation and elasticity and will break rather than stretch when pulled.
When choosing yarn for knitwear,
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In 2016, I received a lovely skein of yarn for Christmas. It was a small skein of a wool, alpaca, and silk blend that seemed perfect for a hat. The hat looked great and was warm, but it had one major issue: it would constantly slip down and cover my eyes. Was there something wrong with the pattern or my knitting? No, it’s that I didn’t understand the mechanical properties of the yarn.
Mechanical properties are how a material reacts when a force is applied to it. If you pull it, does it break? If it stretches, does it go back to its original shape? If it hangs, does it drape well? If you rub it, does it pill? By understanding the mechanical properties of fibers, you can better choose the yarn for your projects and knit garments that turn out how you imagined.
There are many mechanical properties and even more fibers, so this article focuses on the ones most relevant to knitting: tenacity, elongation/elasticity, drape, and abrasion resistance, all in keratin fibers. Keratin is a protein that makes up animal fibers such as wool, alpaca, angora, and mohair. Silk is another animal fiber, but it is made of the protein fibroin, giving silk different properties.
Tenacity
Tenacity is the tensile strength of a fiber—how much force it takes to break the material in relation to its fineness. The tensile strength of a knitting yarn can vary depending on the structure of the yarn, how it was spun, and how the fiber was produced. One of the largest influences is the type of fiber.
In the world of textile fibers, keratin fibers are relatively weak, but they are strong enough for most knitting projects. You need to consider the strength required of your knitted garment. For something like a scarf, tenacity isn't very important. For a pair of socks to survive many hiking trips, the fibers making them up need to be strong. This is why wool socks often have other fibers, such as nylon, blended in to give them strength.
This sock shows signs of wear on the heel.
The tenacity of a fiber can also change depending on whether it is dry or wet. Keratin fibers become weaker in water. Tenacity in water is very important when thinking about how to launder something. Wool objects can be washed in water but should be cleaned gently. Consider how often and how intensely your knit garment will need to be cleaned when choosing your yarn. (You also need to think of felting when considering wool, but that's another topic!)
The easiest way to measure tenacity at home is to try to break the yarn apart with your hands. If it’s really easy to do, it has low tenacity. If it’s impossible, it has high tenacity. Compare your yarn to similar weight yarns in your stash to see how the different fibers change the tenacity. However, it is also important to consider other fiber properties to create your dream knit garment.
Elongation and Elasticity
Elongation and elasticity are two similar properties related to the stretchiness of a fiber. Elongation is how much a fiber can stretch before breaking. Elasticity is the ability of a fiber to return to its original length after stretching. Wool has high elongation and elasticity, meaning that it can stretch quite a lot and return to its original shape. On the other hand, angora rabbit has low elongation and elasticity and will break rather than stretch when pulled.
When choosing yarn for knitwear,[PAYWALL] you should consider how these properties will change the appearance and performance of the object. If you want to make a tight-fitting sweater, wool is a great choice, especially from breeds known for their stretch. Since it has high elongation and elasticity, it would stretch over the body and recover its shape afterward.
Left to right: Bluefaced Leicester wool, mohair, silk, and alpaca fibers. All have different elongation and elasticity.
The elongation and elasticity of a fiber do not always match. Alpaca fibers have high elongation but low elasticity. These fibers will stretch but will not return to their original length. This is what happened with my hat: the fibers stretched but didn’t recover, causing the hat band to widen and fall down. Alpaca is a lovely fiber, but it is better suited to projects that don’t require recovery after stretching, like a shawl.
Measuring these two properties is easy with a ruler. Cut a piece of yarn, tie one end to a stationary object, and measure the length under no tension. Pull the yarn as long as it will go without breaking, and measure the length under this tension to find the elongation. Release the yarn and measure the length under no tension again to find any changes to get the elasticity.
Video by Pamela K. Schultz
Drape
A fiber’s drape is how a textile hangs under its own weight. A garment made from a fiber with good drape is fluid and hangs over the body. Keratin fibers tend to have good drape when knit, but especially angora rabbit, alpaca, mohair, and low-crimp wool. Yarn made from these fibers would be best knit into loose, flowy garments such as shawls and unstructured cardigans.
Fibers with low drape are often described as having structure or body and as stiff. These fibers are more suited for a garment with more structure, such as a jacket.
Both these swatches are knit with Merino yarn, but at different gauges. The swatch on the left is knit at a tighter gauge, and has little drape, while the swatch on the right has more drape.
The best way to see the drape of your yarn is to knit a sample. Does the swatch conform to the shape of anything under it or flop over when supporting its own weight? It has good drape. Is the swatch stiff, and does it obscure anything under it? Then the yarn has low drape but good body.
Abrasion Resistance
Abrasion resistance is a fiber’s ability to resist breaking from friction. Rubbing the surface of a fiber with low abrasion resistance will cause it to become fuzzy, develop pills, and weaken. Conversely, a fiber with high resistance will remain smooth and strong. Often, the softest fibers are also the ones least resistant to abrasion. Luxuriously soft fibers such as angora rabbit and cashmere are the most prone to pilling. Wool with medium to long staple lengths from breeds such as Scottish Blackface, Border Leicester, and the Down sheep are coarser but have much more abrasion resistance.
Closeup of a sweater showing pills on the surface of knit fabric.
Finding the balance between next-to-skin softness and durability can be challenging. For garments that directly touch sensitive skin, such as cowls, it may be best to forgo resistance to abrasion and opt for a soft fiber such as angora. But for clothes that need to be hard-wearing such as an everyday working sweater, it may be best to choose a fiber with high abrasion resistance.
Isabella Rossi runs Rossi Conservation, a textile conservation studio based in Scotland. She is the President of the Edinburgh Guild of Weavers, Spinners, and Dyers, and is constantly crafting. She aims to help textile artists understand and care for the materials they work with. Visit rossiconservation.com
This sock shows signs of wear on the heel. 
Left to right: Bluefaced Leicester wool, mohair, silk, and alpaca fibers. All have different elongation and elasticity.
Both these swatches are knit with Merino yarn, but at different gauges. The swatch on the left is knit at a tighter gauge, and has little drape, while the swatch on the right has more drape. 
Closeup of a sweater showing pills on the surface of knit fabric.