Not all fabrics are made the same and in this post, we are going to break down what gives a fabric its properties, name and functions. All fabrics can be thought of as being the combination of two elements: fiber content and construction. When fibers are constructed using a certain stitch or technique, the result is a piece of fabric. Moreover, when thinking about knits, the type of construction method and fiber content used to manufacture a fabric will change the texture, weight, degree of stretch, as well as, stretch direction.
Understanding that there are several elements that influence the degree of stretch and stretch direction of a knit fabric, confirms the idea that every time you change your fabric, you must re-calculate the stretch ratio and re-draft your slopers/patterns with the corresponding amount of negative ease. Not only does content and construction change the degree of stretch of a fabric, but it will change the stretch direction. The ability to identify the type of knit you are working with, will allow you to properly identify the direction of greatest stretch and the degree of stretch.
When working with knits, you want to ensure the direction of greatest stretch is what will wrap around the body (horizontal measurements). This is done because we want to maintain flexibility in the vertical measurements to account for movement and have a contoured fit in the horizontal measurements. Therefore, when you are calculating negative ease, you must identify the direction of greatest stretch of your knit fabric and conduct your stretch tests in that direction. If you fail to test your fabric using the direction of greatest stretch, you will end up calculating less negative ease than is required. Additionally, if you cannot identify the direction of greatest stretch, you may end up aligning your pattern pieces in the wrong direction when cutting. To sum it up, you must identify the direction of greatest stretch of your knit fabric in order to calculate the correct amount of negative ease to be applied to the horizontal measurements of your slopers and patterns.
Construction Method
The construction method used to manufacture a fabric is what will determine if the fabric falls into one of the three main categories: wovens, knits and non-wovens. In this post, we will be focusing on wovens and knits.
Fiber Content
The fiber contents of a fabric can be divided into three categories: natural, regenerated and synthetic fibers. Natural fibers include examples such as wool, cotton, linen and silk. Regenerated fibers are made from materials such as wood pulp (bamboo, rayon, viscose and modal). While synthetic fibers are formed from chemical compounds (polyester, acrylic, spandex and nylon).
The way in which fiber content and construction method are combined together, will determine if a fabric is a knit or woven and will further determine the properties of a knit or woven.
Before we move on, we will go over some basic definitions to lay the groundwork for knits 101.
What is warp, weft and selvage?
Selvage
When it comes to identifying the selvage, an easy visualization to think of unrolling a roll of fabric forever, the longest edge will be your selvage. The selvage of the fabric is the edge of the fabric, it will typically be identified with some sort of ridging, pattern, discoloration. In both knits and wovens, the selvage aids to stabilize and neaten the edge of fabric for accurate cutting. Why the selvage is important is because you will need to use the selvage to help identify the straight grain/warp or cross-grain/weft of your fabric.
Straight grain or Warp
The straight grain or warp direction of a fabric runs parallel to the selvage, essentially it runs in the same direction of the selvage. In wovens, the straight grain is typically referred to as the warp direction. Whereas, with knits, the warp direction is referred to as the straight grain. In any case, the straight grain or warp direction is what runs in the same direction of the selvage.
Cross-Grain or Weft
The cross-grain or weft direction of a fabric is the opposite of the warp direction, it runs perpendicular to the selvage. For example, when you cut fabric off a roll, you’ll be cutting the fabric in the cross-grain or weft direction. In woven fabrics, this is also known as the weft direction. For knitted fabrics, it's simply called the cross-grain. In any case, the cross-grain or weft direction is what runs perpendicular to the selvage.
Why Woven Fabrics Vary Less Than Knits When It Comes to Ease
When manufacturing woven fabrics, the weaving process requires a strong warp yarn. Whereas, knit fabrics do not require a strong warp yarn and have the flexibility to use a greater variety of yarns in their construction. Since woven fabrics have stronger requirements for their warp yarns than knits, there is less variability in the yarns used for wovens and less variability between woven fabrics as compared to knits. In essence, wovens use a less diverse variety of yarns than knit fabrics. This fact will be relevant when discussing the difference between positive and negative ease between wovens and knits. In short, the negative ease required for a knit fabric will change with each knit, as opposed to woven fabrics which can apply a similar amount of positive ease across multiple fabrics.
Wovens
Since knits are the antithesis of wovens, it is necessary to understand the difference in construction between knits and wovens. Woven fabrics are constructed using a weaving method. To weave fabric, you must intersect two or more yarns at right angles on a loom. The weft yarns run across the fabric and are perpendicular to the selvage while the warp yarns remain parallel to it in a vertical direction. This method of construction gives woven fabrics the properties of sturdiness and minimal stretch.
As we will see with knits, there are different and distinct methods for constructing a woven fabric. With wovens, there are four separate weaving methods used to construct different woven fabric types: satin weave, basketweave, plain weave and a twill weave. Diving into the details of what makes each weave structure distinct is outside the scope of this article but it is important to note that construction method is what results in different fabric types, weights, textures etc.
Knits
In contrast to wovens, which are constructed by interlacing yarns, knit fabrics are created by the interlooping of yarns. Wovens, interlace. Knits, interloop. Similarly to wovens, there are different and distinct methods for constructing knit fabrics. The diversity of knit fabrics is expansive due to the greater range of yarns that can be used in the manufacturing process, as well as, the variety of stitches and number of needles that can be used to construct a knit. Basically, the yarn used and the construction method will impact the degree of stretch and the direction of greatest stretch. Therefore, knits must always be assessed on a case by case basis when calculating negative ease for pattern drafting.
The Different Methods For Producing Knits: Warp and Weft
There are two main stitch types that produce knits, warp knitting and weft knitting. The type of construction method will influence the direction of greatest stretch, the name of a knit and its multiple properties.
Weft Knitting
The method of weft knitting resembles how you would knit a scarf or a sweater when knitting by hand. In weft knitting, a single yarn moves horizontally to create a row of loops. The loops go in the cross-grain direction and use a combination of knit and purl stitches to produce either a single knit or a double knit. Weft knits are unstable, which means they can unravel and do not have good recovery, meaning they will sag if not laundered properly.
Mechanical Stretch
Weft Knits contain a high degree of mechanical stretch and will stretch regardless of yarn type. The interlocking loops of a knit fabric is what gives the fabric its inherent stretch. As the fabric is stretched, the loops expand, giving a weft knit its stretchiness. So, even if a weft knit does not contain spandex, it will still stretch due to how the loops expand and contract when pulled and released. In this case, the loops of a weft knit is what allows for stretch, not the yarn itself. In this case, weft knits will stretch and have elastic properties even when the yarns do not contain lycra (or any other elastic synthetic fiber). However, a weft knit made with a yarn containing a spandex core will have a higher degree of stretch than a weft knit without spandex. This is because not only are the loops stretching but once the loops have reached their maximum degree of stretch, the yarn itself will stretch. For example, a Cotton Spandex Jersey (93% cotton, 7% spandex).
Stretch Direction of Weft Knits
When it comes to stretch direction, weft knits stretch both in the weft/cross-grain and warp/straight grain direction. With weft knits, the direction of greatest stretch (with some exceptions), will be in the weft direction, widthwise and perpendicular to the selvidge (cross-grain).
Weft Knits can be further broken down into two categories, depending on construction method. These two kinds of weft knits include: Single Knits and Double Knits.
Single Knits
Single knits are knitted with a single set of needles and have different right sides and wrong sides. Single knits can be further broken down into two fabric types: Jersey and Sweater knits.
Some examples of the applications for Jersey fabrics include:
- polo-shirts
- T-Shirts, skirts
- Pajamas
- Knit tops,
- Lingerie
- Underwear
- Light weight sweaters
- Dresses.
Some examples of the applications for Sweater knits include:
- sweaters
Double Knit
Double knits are knitted with two needles that work in unison, creating a double thickness. Double knits are two-faced fabrics where both the right side and wrong side of the fabric look the same and have the same vertical ribs (like the right side of a jersey). Due to both sides of the fabric having the same vertical ribs, there is equal tension on both sides of the fabric, creating a more stable fabric. Double knits can be further categorized into three fabric types: Interlock Knits (have limited stretch in the crossgrain direction), Ribbed knits and bottom-weight double knits (Ponte di Roma, Piqué and jacquard).
Some Examples for Ribbed Knits include:
- Collars
- Cuffs
- Waistbands
- Necklines
- Dresses
- Tops
- Lingerie
- Shorts
- Socks.
Some Examples of Interlock Include:
- Lingerie
- Lining
- Backing on bonded fabrics
- Activewear
- Shorts
- Tops
Some Examples of Ponte di Roma Include:
- Pants
- Jackets
- Suits
Warp Knits
Unlike weft knits where loops are formed in a row, warp knitting is done with yarns running vertically from the top of a machine to create loops in a column or lengthwise direction. Warp knits are constructed with looping stitches in the straight-grain (warp) direction, parallel to the selvage. Additionally, warp knits do not use knit or purl stitches in their construction. Stitches are formed with warp knits when one needle moves in a zigzag formation and the loops interlock together. Warp knits pass yarn over several needles at a time, as opposed to weft knits which pass one yarn over one needle at a time. Warp knits are stronger and more stable than weft knits and are less likely to unravel. Due to their stability, warp knits are generally used in technical apparel, sportswear and underwear.
Mechanical Stretch
A major difference between weft and warp knits is the lack of inherent stretch of a warp knit. As mentioned earlier, weft knits have inherent mechanical stretch due to the way in which the loops naturally expand when stretched. Unlike weft knits that will stretch regardless of yarn type, warp knits have minimal mechanical stretch. Therefore, for a warp knit to stretch, yarn type is critically important. Therefore, spandex must be incorporated in order for the warp knit to have elasticity and stretch.
On the topic of yarn type, warp knits only use multifilament yarns. This means, warp knits use yarn containing more than one filament fiber (filament fiber: continuous hairlike strands). With the use of multifilament yarns, such as core-spun yarn coiled around an elastic core, there is more flexibility in the yarn, resulting in elasticity in the fabric.
To recap, warp knits do not have inherent mechanical stretch and the yarn type is what allows for warp knits to stretch. If core-spun yarn coiled around an elastic core is used in the production of a warp knit, the resulting fabric will have elasticity.
Stretch Direction
The main takeaway with warp knits is the direction of greatest stretch. Remember, warp knits have a minimal amount of mechanical stretch and therefore the addition of spandex fibers is what will give a warp knit its stretch.
Warp knits typically have very limited stretch in the lengthwise direction (warp), as they are primarily made up of lengthwise yarns (warp yarns) that are interlooped in the knitting process. The direction of greatest stretch in warp knits is usually in the widthwise/weft direction (across the fabric), which is perpendicular to the warp yarns. Therefore, it is important to identify the direction of greatest stretch when working with warp knits and cut the fabric accordingly.
Remember, when we are designing with stretch, we want the direction of greatest stretch to wrap around the body. Therefore, when you are working with a warp knit, you must conduct your stretch test and cut your fabric perpendicular to the selvage.
An important note, knowing whether you are working with a weft or warp knit can help serve as a starting point when determining the direction of greatest stretch. However, since there is so much variability with knit fabrics in terms of yarn and construction, it is prudent to consult the technical sheet of your fabric to determine stretch direction. Furthermore, it can be helpful to conduct a stretch test in both the warp and weft direction to see which direction has more stretch. Sometimes the fabric will let you know which direction it prefers!
Tricot and Rachel
Similar to weft knits, warp knits can be further broken down into two types of knits depending on construction method. These two different categories of warp knits include: Tricot Knits and Rachel Knits.
Tricot Knits
If you are creating stretch garments for dance, gymnastics or even swimwear, then tricot knits are your bread and butter. Tricot knits are used in interlinings, lingerie, underwear, lining, swimwear and athletic apparel.
When it comes to the appearance of a tricot, the right side of a tricot will have a dull surface and vertical ribs, like a jersey fabric and the wrong side of a tricot will have a shiny surface and a horizontal zigzag loop formation. With tricot knits, the way in which the stitches are knit results in a smooth surface where stitches are closely packed using fine gauge needles. The combination of a smooth surface, tightly knit stitches and its ability to quickly dry when wet, makes tricot an ideal fabric for activewear and swimwear.
Some Examples for Tricot include:
- Interlinings
- Lingerie
- Underwear
- Lining
- Swimwear
- Athletic Apparel
Raschel Knit
There are six categories of raschel knits: raschel knit, raschel lace knit, netting, mesh, powernet and thermal knit.
The most pertinent types of raschel knits when it comes to stretch pattern making will be mesh and powernet. Mesh has open holes and the front and back side look the same. Powernet is an elastic mesh with open holes and front/back look the same.
Knits 101 is all about understanding the different properties of fabrics and how to calculate negative ease when working with knits. It is important to identify the direction of greatest stretch in order to have a contoured fit in the horizontal measurements. When calculating negative ease, you must take into account the content and construction of the knit fabric to get the correct amount.
Conclusion
In this post, we’ve walked you through the basics of wovens, weft and warp knits and how to identify stretch direction to properly calculate the degree of stretch.
Woven fabrics are made on a loom with yarns intersecting at right angles. The weft yarns run perpendicular to the selvage while the warp yarns remain parallel to it in a vertical direction. This method of construction gives woven fabrics the properties of sturdiness and minimal stretch.
Weft knits are fabrics that are created by interlocking loops of yarn. The stretchiness of weft knits is due to the way the loops expand and contract when pulled and released. Weft knits can stretch in both the warp/straight grain direction and the weft/cross-grain direction. Warp knits have a minimal amount of mechanical stretch and therefore the addition of spandex fibers is what will give a warp knit its stretch. With a warp knit, the direction of greatest stretch will be in the weft direction, parallel to the selvage (but always test for yourself!).
In order to get the perfect fit when working with knits, it is important to understand how different elements like fiber content and construction can affect a fabric's stretch. By identifying the direction of greatest stretch and applying negative ease in that direction, you can create patterns that contour to the body. Remember, the direction of greatest stretch of a fabric will wrap around the horizontal measurements of the body. Keep in mind that every time you change your knit fabric, you must recalculate the stretch ratio and re-draft your slopers/patterns!
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