Weft knitted structures, especially those used for hosiery, knitwear and underwear, have unique properties of form-fitting and elastic recovery based on the ability of knitted loops to change shape when subjected to tension. Unfortunately, dimensional changes can also occur during production, or washing and wearing, when problems of shrinkage and size variation can cause customer dissatisfaction and increased production costs.
During the 1950s, HATRA (the Hosiery and Allied Trades Research Association) investigated the problems of knitted garment size variation and created a much clearer understanding of the influence of stitch length on knitted fabric dimensions, which led both to further research in this field and to the practical application of this knowledge in production. Doyle  emphasized the relationship between stitch length and fabric dimensions when, in plotting stitch length against stitch density for a wide range of dry, relaxed, plain weft knitted structures, he showed that, irrespective of yarn type or count or of machine type or gauge, the points lay close to a general curve. HATRA was thus able to establish three basic laws governing the behavior of knitted structure:
1 Loop length is the fundamental unit of weft knitted structure.
2 Loop shape determines the dimensions of the fabric, and this shape depends upon the yarn used and the treatment that the fabric has received.
3 The relationship between loop shape and loop length may be expressed in the form of simple equations.
The acceptance of these rules has encouraged the introduction of yarn loop-length measuring and yarn feed control devices, has accelerated improvements in shrink-resist and fabric relaxation treatments, and has provided a basis for the theory of knitted fabric geometry.
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