Most synthetics have a tendencyto "rebound" after being worked like braiding. That is the shrinkage that occurs. Weathering the material after it has been worked (getting it wet, air drying it), can accelerate the rebounding process. As a rule, leave a newly completed braiding project sit for 24 hours before putting the finishing knot or trimming the ends short. Any further material recovery after that time will be negligible. You've just got to let the project rest for a bit is all.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)