What makes a trampoline boncy?

The 'bounce' of a trampoline is generated by the movement of the trampoline springs, situated around the frame of the trampoline and connected to the trampoline bed.

The more trampoline springs that a trampoline has, the better bounce the trampoline will generate. The quality and effectiveness of a trampolines' bounce is also impacted by the amount of movement there is on the bed, more weight again generates more bounce.