Fleece is a knit fabric, not a woven one. The soft, fuzzy texture might make it hard to tell, but underneath that brushed surface is a knitted base, typically produced on circular knitting machines that create large, continuous sheets of fabric.
How Fleece Is Constructed
Fleece starts as a knit fabric made from interlocking loops of yarn, most commonly polyester. Circular knitting machines produce the base material in a specific structure called a three-thread weft knit. This structure has three distinct layers: an outer layer, a binding layer in the middle, and an inner fleece yarn layer. The fleece yarn periodically forms tuck loops, creating a textured inner surface that becomes the foundation for that characteristic softness.
After knitting, the fabric goes through a finishing process called napping or brushing. Machines agitate the surface fibers, pulling them up and disrupting the tight loop structure to create a raised, fuzzy pile. The raised fibers are then trimmed to a uniform height. Some fleece fabrics are brushed on both sides for maximum softness, while others are brushed on just one. This finishing step is what makes fleece look and feel so different from a typical knit like a t-shirt jersey, and it’s the reason people often can’t tell what the underlying structure is.
Why Knitting Matters for Fleece Performance
The knit structure is not just a manufacturing choice. It gives fleece several properties that a woven fabric wouldn’t provide as easily. Knit fabrics are made of interlocking loops rather than a rigid grid of perpendicular threads, which means they naturally stretch and recover. That’s why a fleece pullover moves with your body rather than feeling stiff.
Breathability is another direct benefit. The open structure of a knit allows air to flow through more easily than tightly woven materials. This helps regulate body temperature: the trapped air pockets in the brushed pile keep you warm, but the knit base lets excess heat and moisture escape. That combination is why fleece works well for both active outdoor use and casual layering. You stay warm without overheating.
Fleece Fiber Content
Most fleece you’ll find in stores is 100% polyester, especially the polar fleece used in jackets, vests, and blankets. Polyester fleece dries quickly, retains almost no water, and holds up well to repeated washing. Many outdoor brands also offer fleece made from recycled plastic bottles, which uses the same knitting and brushing process but with recycled polyester yarn.
Cotton fleece and cotton-polyester blends also exist, commonly used in sweatshirts and hoodies. These are built on the same three-thread knit structure but feel heavier and more absorbent than polyester versions. Common blends include 80% cotton with 20% polyester, and 60% cotton with 40% polyester. Pure cotton fleece allows the most airflow, while adding polyester increases thermal resistance, meaning it holds heat more effectively. An 80/20 cotton-polyester blend, for example, showed dramatically higher thermal resistance than 100% cotton in textile testing, despite being less breathable.
How to Tell Knit From Woven
If you’re trying to identify whether any fabric is knit or woven, there are a few quick tests. Knit fabrics stretch, especially in one direction, because their loop structure can expand and contract. Woven fabrics have very little give unless they contain spandex or a similar stretch fiber. Pull a piece of fleece sideways and you’ll feel it stretch easily, confirming its knit construction.
You can also look at the back of the fabric. On fleece that’s only brushed on one side, the reverse often shows a smoother surface where you can make out the knit loop pattern. On double-brushed fleece, both sides are fuzzy, making it harder to see the structure, but the stretch test still works. Woven fabrics, by contrast, have a visible grid pattern of threads running in two perpendicular directions, and they resist stretching on those axes.
The Woven Exception
There is one type of fleece that blurs the line. Some specialty fleece fabrics, particularly certain sherpa and high-pile varieties, start with a woven base instead of a knit one. In this process, loop piles are woven into the base fabric, then cut and raised to create the fuzzy surface. This approach is less common than knit fleece and typically produces a heavier, less stretchy fabric. Unless a product specifically notes a woven construction, the fleece you encounter in most clothing and blankets is knit.