Like weaving, knitting is a technique for producing a
two-dimensional fabric made from a one-dimensional yarn or thread. In weaving,
threads are always straight, running parallel either lengthwise (warp threads)
or crosswise (weft threads). By contrast, the yarn in knitted fabrics follows a
meandering path (a course), forming symmetric loops (also called bights)
symmetrically above and below the mean path of the yarn.
These meandering loops
can be stretched easily in different directions, which gives knitting much more
elasticity than woven fabrics; depending on the yarn and knitting pattern,
knitted garments can stretch as much as 500%. For this reason, knitting was
initially developed for garments that must be elastic or stretch in response to
the wearer's motions, such as socks and hosiery.
For comparison, woven garments
stretch mainly along one direction (the bias) and are not very elastic, unless
they are woven from stretchable material such as spandex. Knitted garments are
often more form-fitting than woven garments, since their elasticity allows them
to follow the body's curvature closely; by contrast, curvature is introduced
into most woven garments only with sewn darts, flares, gussets and gores, the
seams of which lower the elasticity of the woven fabric still further. Extra
curvature can be introduced into knitted garments without seams, as in the heel
of a sock; the effect of darts, flares, etc. can be obtained with short rows or
by increasing or decreasing the number of stitches. Thread used in weaving is
usually much finer than the yarn used in knitting, which can give the knitted
fabric more bulk and less drape than a woven fabric.
If they are not secured, the loops of a knitted course will
come undone when their yarn is pulled; this is known as ripping out,
unravelling knitting, or humorously, frogging (because you 'rip it', this
sounds like a frog croaking: 'rib-bit'). To secure a stitch, at least one new
loop is passed through it. Although the new stitch is itself unsecured ("active"
or "live"), it secures the stitch(es) suspended from it. A sequence
of stitches in which each stitch is suspended from the next is called a wale. To
secure the initial stitches of a knitted fabric, a method for casting on is
used; to secure the final stitches in a wale, one uses a method of binding off.
During knitting, the active stitches are secured mechanically, either from
individual hooks (in knitting machines) or from a knitting needle or frame in
hand-knitting.
