In an earlier article regarding the shrinkage of cotton ( Why Cotton Shrinks), the general causes were discussed. There is an excellent study done by Veena Verma of BMN College which looks in depth across the various factors related to yarn that leads to shrinkage. She tested 24 samples from very light weight to heavy weight for dimensional stability after soaking and 25 washings and the following are some very useful insights from the studies:
1. Basic reason for shrinkage is the relaxation which is the tendency of the yarn to revert to its normal and un stretched dimensions this is called relaxation shrinkage. Most fabrics are produced under tension which leave strains in the fabric. Usually several cleanings are required to relax it completely.
2. When the yarns are wet, they swell, and consequently the warp thread has a longer bending path to take round a swollen weft thread. The warp length must either increase in length or alternatively, the weft threads must move close together.
3. Fabrics shrinks after soaking and percentage significantly increases after repeated washing.
4. The ends per inch and shrinkage are inversely related. As the number of ends increase, shrinkage percentage decreases. There is no clear trend between shrinkage and picks per inch. This is true for both soaking and washing.
5. Higher the number of Ends per inch than picks per inch, shrinkage values are reduced.
6. More the cloth cover, less is the warp way and weft way shrinkage on soaking, this is not true for washing.
7. The fabric with coarse yarn count has more shrinkage and fabrics with finest count have the lowest shrinkage.
8. More the twist multiplier, higher is the shrinkage on washing.
9. There is no correlation in cloth weight and thickness on shrinkage.