Properties of fabrics
The topology of a knitted fabric is relatively complex. Unlike woven fabrics, where strands usually run straight horizontally and vertically, yarn that has been knitted follows a loopy path along its row, as with the red strand in the picture below , in which the loops of one row have all been pulled through the loops of the row below it.
Because there is no single straight line of yarn anywhere in the pattern, a knitted piece can stretch in all directions. This elasticity is unavailable from woven fabrics, which only stretch along the bias. Many modern stretchy garments, even as they rely on elastic synthetic materials for some stretch, also achieve at least some of their stretch through knitted patterns.
Basic knitted fabric (as in the diagram, and usually called a stocking or stockinette pattern) has a definite right and wrong side. On the right side, the visible portions of the loops are the verticals connecting two rows, arranged in a grid of V shapes. On the wrong side, the ends of the loops are visible, both the tops and bottoms, creating a much more bumpy texture sometimes called reverse stockinette stitch. (Despite being the "wrong side," reverse stockinette is frequently used as a pattern in its own right.) Because the yarn holding rows together is all on the front, and the yarn holding side-by-side stitches together is all on the back, stockinette fabric has a strong tendency to curl toward the front on the top and bottom, and toward the back on the left and right side.
Stitches can be worked from either side, and various patterns are created by mixing regular knit stitches with the "wrong side" stitches, known as purl stitches , either in columns ( ribbing), rows ( garter, welting ), or more complex patterns. Each such fabric has different properties: a garter stitch has much more vertical stretch, while ribbing stretches much more horizontally. Because of their front-back symmetry , these two fabrics have little curl, making them popular as edging, even when their stretch properties are not desired.
Different combination of knit and purl stitches, along with more advanced techniques, generate fabrics of considerably variable consistency, from gauzy to very dense, from highly stretchy to relatively stiff, from flat to tightly curled, and so on.