An elasticity hair test determines the hair tensile strength.
To do the test, remove a strand of hair from the side of the head above the ears. Hold the hair between your thumb and forefinger.
With the thumbnail and index of nail of the other hand, run the distance of the hair rapidly, as you would curl a ribbon with scissors.
This should create a series of small curls.
Gently pull the hair straight for 10 seconds and release. If the hair completely or almost completely returns to the curl pattern, it has good elasticity. If it returns only 50% or less, it is structurally weak and may require protein or other deep conditioning treatments.