Knit fleece is one of the most popular fabrics in the world. It is used in sweatshirts, pullovers, and activewear because it is inexpensive, soft, and has a smooth finish perfect for screen printing or embroidery. Almost everyone has at least one item in their closet made from knit fleece, but few of us have put much thought into how it is actually made.
While knit fleece may seem simple, it really isn’t at all when you consider the manufacturing process and the many variables that go into making it high quality. Many manufacturers today have not only changed their knitting processes in order to achieve better, more high-quality products, but they have also added “extras” in the garment, such as Lycra in the rib trim and decorative stitching.
When the cotton comes to the factory
The process begins with bales of cotton, which are laid down so the cotton can be blended together. The cotton is opened, and then filtered; pulling out foreign materials and getting the cotton to form more uniform strands. This is the step that brings staple fiber into a form that can be reduced in bulk and eventually twisted into a spun yarn. Next, the cotton goes through a drawing process, which increases the length per unit weight of the strands. Then, depending on the spinning system employed to make yarn, the cotton must go through various other processes.
There are three spinning systems that create the yarn used in fleece; open-end spinning, ring spinning and airjet spinning. Open-end spinning is popular because it is less expensive. The drawback is that fabric made from open-end yarn tends to be rougher than that made from other methods has a harsher feel. Ring-spun products are softer and have a nicer hand. Sweatshirts made with air-jet spun yarns, are becoming more popular because the air jet yarns are less hairy than their counterparts. Because of this, fabric pilling is greatly reduced. (Pilling is caused when cotton fibers loosen on a fabric and get hung up on fibers protruding from the surface of that fabric. If the loose fiber doesn’t break off, it forms a pill.) Air-jet spun yarns are used only in cotton/polyester blends, however.
Knitting the yarn
The knitting of fleece fabric is performed on a four-track knitting machine. Fleece can be either two-end or three-end constructions. The difference between the two is in the number of yarns knit into the fabric. Higher-end sweats are usually three-end fleece, meaning that the mill uses a face yarn, a backing yarn and a tie yarn that interweave and create a nap. Three-end fleece is considered more stable and durable because it uses three yarns in the knitting process as opposed to two. Two-end fleece does not use the tie yarn in knitting and, therefore, does not have as smooth a face as three-end. You end up with less thickness on a two-end fleece product than a three-end product.
After knitting, the greige, or unfinished, fabric is rolled onto large rolls. These rolls are batched together for wet processing. Excess oil, waxes and dirt, are typically extracted at this point, after which the fabric is stabilized and prepared for either bleaching (for white fleece) or dyeing. Typically, the body and rib fabric are bleached and dyed together to ensure color compatibility. The fabric content and color determines how long the fabric stays in the dye vats. At the end of the dye or bleach process, the fabric is rinsed to remove excess dye, then it goes through an extractor, which functions like an old-fashioned washing machine where water is squeezed out under a continuous rolling device. Fabric softeners can be added at this point.
The fabric is then turned inside out to prepare it for napping.The napping machine is a large drum with rollers on the outside of it. The wire bristles on those rollers alternate between straight and bent bristles. Straight wires called travelers move the fabric around the drum. The bent bristles actually nap the fleece by grabbing the loops and breaking them, creating the fuzz on the underside of the fabric.
After napping, the fabric is turned right-side out and either calendared or compacted to reduce shrinkage. Calendaring is a process of spreading the fabric to its desired width and squeezing it between metal rollers with steam present to stabilize the fabric,
During compaction, fabric is fed into a heated machine to compact or push the loops in the fabric closer together. Basically, the fabric is going into the compaction chamber faster than it is coming out, so the fabric is being pushed together. An added benefit of compacting is that it softens the fabric.
Once the fabric has reached this stage, it has become ready to be cut and sewn into the custom embroidered sweatshirts, sweatpants, pullovers we wear every day. By knowing a little bit more about the manufacturing process behind the knit fleece itself, you may have a little better understanding when shopping for the clothes made from it.