Woven and knitted goods are 3-dimensional arrays
of crimped yarns. Fabric forming processes take straight lengths of yarns and
force them into 2-dimensional crimped lengths. The degree of crimp is a
function of the yarn size and fabric construction.
When fabric is completely
relaxed, the crossing yarns will move around in relation to each other until a
stable configuration is reached. This stable arrangement, the point where the
relaxed fabric no longer shrinks in width and length, is also related to yarn
sizes and fabric construction. When stretching tensions are applied to the
fabric, the crimped amplitude decreases and the fabric grows in the direction
of the stress.
Later when the tensions are relieved and the fabric allowed relaxing,
the crimp amplitude returns to its stable configuration and the fabric shrinks.
Many fabrics are stretched during wet processing as they are pulled from one
operation to another. This
is the major cause of fabric shrinkage. 
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