Knit fabric can be made from almost any fiber, natural or synthetic. What makes it “knit” isn’t the material itself but the structure: a continuous length of yarn formed into rows of interlocking loops, rather than the over-under weaving pattern of woven fabrics. Those loops are what give knit fabric its signature stretch and softness. The fibers chosen for the yarn determine everything else, from how the fabric breathes to how long it lasts.
How Knit Fabric Gets Its Structure
In a woven fabric, two sets of yarn cross over and under each other in a grid. Knit fabric works differently. A single yarn is pulled through itself again and again to create columns of vertically intermeshed loops, built up row by row. Each loop hooks through the one below it, forming a flexible chain that can stretch in multiple directions and spring back into shape. This is why a cotton t-shirt feels so different from a cotton dress shirt, even though both are made of the same fiber. The loop structure, not the raw material, is what defines a knit.
Natural Fibers
Cotton is one of the most common fibers knitted into fabric. It’s soft, breathable, hypoallergenic, and works for everything from lightweight summer tees to structured cable-knit sweaters. Its smooth surface gives clean stitch definition, which is why cotton knits tend to look crisp and even. The tradeoff is durability: cotton is a short-staple fiber, meaning its individual strands are relatively short with more exposed ends. Those loose ends can work free from the yarn surface through friction, which is why cotton knits are more prone to pilling over time.
Wool is the other major natural fiber in knits. It has a built-in moisture management system: the inside of each fiber absorbs water, while the outside is coated in lanolin, a waxy substance from sheep’s skin that repels it. This means wool pulls sweat away from your body while resisting rain on the surface. Finer wools like merino feel softer against the skin but can pill more easily if the yarn isn’t tightly spun, since those fine, short fibers are easier to dislodge. Coarser, longer-staple wools are more durable but scratchier.
Silk and linen show up in knits less frequently. Silk is a continuous filament fiber, meaning each strand is extremely long with very few exposed ends, so it resists pilling well and drapes beautifully. Linen knits are breathable and get softer with washing, but they have less natural stretch than cotton or wool.
Synthetic Fibers
Polyester is the workhorse of synthetic knit fabrics. It’s lightweight, resists wrinkles, dries fast, and holds its shape through repeated washing. On its own, polyester is hydrophobic, meaning it repels water rather than absorbing it. To make it work as activewear, manufacturers either apply a hydrophilic (water-attracting) coating to the fiber surface or blend it with absorbent fibers. Some performance knits use a dual-layer approach: a hydrophobic inner layer next to the skin pushes moisture outward, while a hydrophilic outer layer pulls it to the surface where it can evaporate.
Another engineering trick for moisture-wicking knits is changing the shape of the fiber itself. Instead of round cross-sections, manufacturers extrude polyester fibers in triangular, cross-shaped, or other irregular profiles. These shapes create tiny channels along the fiber that move sweat through capillary action, no chemical treatment needed.
Nylon is strong and elastic, commonly used in activewear and hosiery knits. Acrylic mimics wool’s warmth and softness at a lower price point, though it pills more easily. Rayon, technically a semi-synthetic made from wood pulp, shows up in knits that need a silky drape without the cost of silk.
How Elastane Creates Stretch
Most knit fabrics stretch to some degree because of their loop structure, but adding elastane (also sold as spandex or Lycra) dramatically increases both stretch and recovery. In a typical elastic jersey knit, two, three, or four yarns interloop in each horizontal row, with only one of those yarns being elastane. The rest are your base fiber, whether that’s cotton, polyester, or nylon.
The percentage of elastane varies widely depending on the end use. Everyday t-shirts and casual tops might contain 2 to 5 percent. Athletic leggings and swimwear typically run higher. Research on elastic jersey knits has tested elastane content ranging from 14 percent up to 43 percent, with higher percentages producing dramatically more stretch. At 14 percent wrapped elastane, the elastic limit sat around 50 to 73 percent elongation depending on direction. At 43 percent bare elastane, the fabric stretched to nearly 120 percent of its original length before losing its ability to snap back. Compression stockings and mountaineering base layers sit at opposite ends of this spectrum, each tuned to a specific level of pressure and recovery.
Blends and Why They Matter
Pure single-fiber knits are relatively rare in commercial clothing. Most knit fabrics are blends designed to combine the best properties of multiple fibers. A 50/50 cotton-polyester jersey gives you cotton’s softness and breathability alongside polyester’s wrinkle resistance and shape retention. An 80/20 polyester-recycled polyester blend performs comparably to virgin polyester in bursting strength, abrasion resistance, and dimensional stability, with a smaller environmental footprint. Testing on 100 percent recycled polyester knit fabric has found it particularly well suited to active sportswear because of its high air permeability and resistance to heat and water vapor.
Common Types of Knit Fabric
The fiber content tells you what a knit is made of. The knit type tells you how those loops are arranged.
- Single jersey is the most common knit structure, lightweight with one smooth side and one textured side. Most t-shirts are single jersey.
- Rib knit has alternating columns of raised and recessed stitches, creating vertical ridges. It’s highly stretchable and is the standard for cuffs, collars, and waistbands.
- Interlock knit is essentially two layers of rib knit locked together, making it smooth on both sides and thicker than jersey. It’s more stable, with less curl at the edges.
- French terry has a smooth outer face and soft loops on the inside, used for sweatshirts and joggers.
- Fleece starts as a knit base, then has its inner surface brushed or napped to create a fuzzy, insulating pile.
Fabric Weight and What It Tells You
Knit fabrics are measured in GSM (grams per square meter), and the number gives you a reliable preview of how the fabric will feel and perform. Lightweight knits in the 120 to 150 GSM range feel airy and are best for summer wear, though they’re less opaque and less durable. The 160 to 200 GSM range hits the sweet spot for everyday t-shirts and casual tops, balancing comfort with enough body that the fabric doesn’t feel flimsy. Polos and activewear tend to land in the 180 to 250 GSM range.
Once you get above 250 GSM, you’re in sweatshirt and hoodie territory. Fabrics from 250 to 300 GSM offer moderate warmth and still flex well for layering. The 300 to 350 GSM range provides serious structure and insulation for cold weather and athletic outerwear. The tradeoff is breathability: heavier knits trap more heat, which is the point in winter but a liability in warmer conditions.
How Knits Are Manufactured
Two main types of machines produce knit fabric, and each is suited to different products. Circular knitting machines feed up to 32 separate yarns into a spinning needle bed that knits continuously in the round, producing a tube of fabric. That tube is then cut open and used as flat yardage for cut-and-sew garments like t-shirts, underwear, and leggings. Circular machines have high output and dominate mass production.
Flatbed knitting machines move yarn back and forth across a horizontal needle bed, building fabric in flat panels. Output is much lower than circular machines, but flatbed knitting can shape individual garment pieces directly on the machine, reducing waste. This is the method behind “fully fashioned” sweaters and knitwear where each panel is knit to shape rather than cut from a larger piece of fabric.
Why Knit Fabrics Pill
Pilling happens when loose fiber ends work their way to the fabric surface through friction, then tangle together into small balls. Fiber length is the biggest factor. Short-staple fibers like standard cotton and many wools have more exposed ends per inch of yarn, giving them more opportunities to snag and clump. Long-staple fibers and continuous filaments like silk have far fewer exposed ends and pill less as a result. High-quality long-staple cotton behaves similarly, with fibers twisted more securely into the yarn so they’re less likely to work loose. Tighter yarn twist also helps, which is why a tightly spun merino sweater will outperform a loosely spun one in pill resistance, even though the fiber is identical.