The hair's elasticity is the measure of how much the hair will stretch (and return to a normal state). Healthy hair, when wet, will stretch up to 50% of its original length and return to its normal shape without breaking, while dry hair will only stretch about 20%.
Elasticity is rated as being low, normal, or high. Hair's elasticity comes from the side bonds in the hair shaft. Hair with normal and high elasticity is easily styled with wet-roller sets, thermal styling tools, etc., while hair with low elasticity may prove hard to curl, or lose its curl quickly.
To test the elasticity of your hair, you need to select strands of hair from four different areas on the head. Be sure the hair is wet. Hold the strand securely and stretch the hair. If the hair stretches and returns to its original length when released, then it has good elasticity. If the hair breaks or doesn't return to its former shape, you have low elasticity.
Hair with low elasticity is highly susceptible to breakage, will be hard to curl, and will not perm well.
Hair wave pattern