Knit fabrics are textiles made by interlocking yarn into connected loops, rather than weaving two sets of threads over and under each other. This looped structure is what gives knits their signature stretch and flexibility. If you’ve ever worn a t-shirt, leggings, or a sweater, you’ve worn a knit. They make up the majority of casual and activewear clothing today, and understanding how they work helps whether you’re shopping for clothes, learning to sew, or just curious about what your wardrobe is actually made of.
How Knit Fabrics Are Made
The core idea behind knitting is simple: instead of crossing threads over and under each other (like weaving does), a knitting machine or hand knitter pulls yarn through existing loops to create new ones. Each loop hooks into the loop below it, building row by row into a stretchy, flexible sheet of fabric. This interlocked loop structure is the reason knits move with your body in a way that woven fabrics like cotton broadcloth or denim simply can’t.
The loops also explain some of knit fabric’s quirks. Because the yarn can shift within each loop, knits have a looser internal structure than tightly woven materials. That looseness gives fibers more room to rub against each other, which is why knit sweaters and activewear can pill up to three times faster than woven fabrics. It’s not a defect; it’s a trade-off for all that stretch and comfort.
Weft Knits vs. Warp Knits
All knit fabrics fall into two broad categories based on the direction the yarn travels during construction.
Weft knits are made with a single yarn looped horizontally, one row at a time, with each row building on the one before it. This is what hand knitting produces, and it’s also how most t-shirt and sweater fabrics are made industrially. A horizontal row of loops is called a “course,” and a vertical column of loops is called a “wale.” Weft knits stretch in both directions, though they typically stretch more side to side than up and down. They can unravel if a loop breaks, which is how runs form in stockings.
Warp knits are made with many parallel yarns looped vertically at the same time by a machine. You can’t warp knit by hand. The result is a fabric that’s generally smoother, flatter, and more stable than weft knits. Warp knits resist runs, don’t unravel, and have little or no vertical stretch, though they can stretch sideways depending on the construction. Most warp knits end up in lingerie, swimwear linings, and athletic mesh.
Common Types of Weft Knits
Single Jersey
Jersey is the most common knit fabric you’ll encounter. It’s a single-layer fabric with a smooth face (the V-shaped loops you see on the outside of a t-shirt) and a slightly textured back. Jersey is thin, breathable, and absorbs moisture well, which is why it’s the go-to for t-shirts, underwear, and lightweight dresses. A plain jersey for summer t-shirts can stretch 150 to 250% horizontally and 50 to 150% vertically before breaking, so it has a significant amount of give.
The downsides: jersey curls at the edges (a headache for sewers), and the loops can skew slightly during washing, which is why some cheaper t-shirts twist at the side seams over time.
Rib Knit
Rib knit alternates columns of loops facing forward and backward, creating visible vertical ridges on both sides of the fabric. This structure makes rib knits extremely stretchy widthwise, which is why they’re used for cuffs, neckbands, and waistbands that need to expand and snap back. Rib knits are thicker than jersey and don’t curl at the edges, but they’re less dimensionally stable overall.
Interlock
Interlock is essentially two layers of rib knit meshed together into a single, double-faced fabric. Both sides look smooth and identical, like the front of a jersey. It’s softer, thicker, and more stable than either jersey or rib knit. Interlock doesn’t curl at the edges and holds its shape better after washing, making it a popular choice for higher-quality t-shirts, baby clothes, and structured knit garments. The trade-off is less stretch than single jersey.
Common Types of Warp Knits
Tricot is the most widely produced warp knit. It’s lightweight (often under 135 grams per square meter), with fine vertical ribs on the face and horizontal ribs on the back. Tricot is silky smooth and drapes well, so it shows up in lingerie, linings, and lightweight sleepwear. About half of all tricot machines produce plain, unadorned fabric, though patterned versions exist.
Raschel knits use coarser yarns and tend to be more open and textured than other warp knits. They’re the technology behind lace fabrics, mesh, crochet-look materials, and many technical textiles like netting and geotextiles. If you’ve seen an open-weave curtain panel or a stretchy lace overlay, it was likely a raschel knit.
Fabric Weight and What It Means
Knit fabrics are classified by weight in grams per square meter (GSM), which tells you far more about a fabric’s behavior than its fiber content alone.
- Lightweight (100 to 170 GSM): Thin, drapey knits like tissue-weight jersey and Tencel jersey. Best for summer tops, t-shirts, and flowy dresses.
- Midweight (170 to 340 GSM): The workhorse range. Bamboo jersey, cotton-blend jersey, and rib knits live here. Suitable for year-round tops, pants, and structured dresses.
- Heavyweight (340 GSM and up): Ponte, fleece, sweater knits, and double knits. These hold their shape well and work for cozy sweaters, jackets, and structured garments that don’t need a lining.
When a knit feels substantial and holds its shape when you drape it over your hand, it’s likely midweight or above. When it feels almost sheer and collapses into folds, you’re in lightweight territory.
Fiber Content and Stretch
Knit fabrics can be made from virtually any fiber: cotton, polyester, wool, rayon, nylon, bamboo, or blends of several. The fiber determines how the fabric feels, breathes, and washes, while the knit structure determines how much it stretches.
Adding elastane (the stretchy fiber sold under brand names like Lycra or Spandex) dramatically changes a knit’s behavior. A plain cotton jersey without elastane will stretch and recover reasonably well, but over time it bags out at the elbows and knees. Adding even a small percentage of elastane improves recovery, meaning the fabric snaps back to its original shape after stretching. Activewear and yoga pants typically contain 10% or more elastane for that compressive, body-hugging fit. Swimwear blends often push to 20% or higher for maximum stretch recovery in wet conditions.
The difference is measurable. In testing, knit fabrics without elastane recovered only about 18% of their stretched length in the vertical direction, while knits with higher elastane content recovered up to 86%. That’s the difference between a t-shirt that gradually stretches out and leggings that hold their shape through hundreds of wears.
Knits vs. Woven Fabrics
The easiest test: pull the fabric sideways. If it stretches noticeably, it’s a knit. Woven fabrics have almost no give on the straight grain (though they stretch diagonally on the bias). Beyond stretch, knits conform to body curves naturally, which is why they dominate in clothing that needs to fit closely without darts or complex tailoring. A woven button-down shirt requires shaping through seams and darts; a knit t-shirt simply stretches to accommodate your body.
Knits also wrinkle less than most wovens because the loops shift and redistribute tension rather than creasing sharply. On the other hand, knits can be more delicate. The loop structure means a snagged thread can pull a visible loop to the surface, and the looser construction makes them more prone to pilling with repeated friction. Warp knits are the exception here, resisting both runs and unraveling due to their interlocked vertical construction.
Practical Uses by Type
Knowing which knit is which helps you pick the right fabric for the job, whether you’re sewing or shopping.
- Jersey: T-shirts, casual dresses, underwear, bedsheets
- Rib knit: Cuffs, waistbands, fitted tops, tank tops
- Interlock: Baby clothing, polo shirts, higher-end t-shirts, structured knit dresses
- Ponte: Work pants, blazers, skirts (a thick double knit with a firm hand)
- Fleece: Sweatshirts, blankets, cold-weather layers
- Tricot: Lingerie, linings, lightweight sleepwear
- Power mesh and nylon/elastane blends: Swimwear, dancewear, compression garments
The knitting industry is also moving into areas far beyond clothing. Researchers are developing 3D knitting techniques that can create solid, shaped objects rather than flat sheets, with potential applications in medical devices like scaffolds for growing artificial ligaments or blood vessels. The same loop-based flexibility that makes a comfortable t-shirt turns out to be useful when you need a structure that can flex and stretch inside the human body.