Popular hardness barometer.
The hardness is tested with a static hardness measurement. This measurement does not take time and speed of acceleration into consideration.
Elasticity stands for bouncing force generated when a tip impacts a cue ball with the speed of acceleration.
When elasticity of a tip gets higher, the contact time of the tip and cue ball gets longer so that you can have more spin on a cue ball and feel bouncy shot feeling.
On the other hand, the contact time is shortened as elasticity gets lower. So that you can get a more solid shot feeling.