The factor which determines if a Rebounder is a bad, ordinary or high quality is the "bouncing amptitude". Let me explain: In the picture above you see four different colored lines which are all moving in an arch above and below a horizontal line. These lines demonstrates the movement of different Rebounder mats while bouncing. The part above the horizontal line shows the up-movement of bouncing and the part below the horizontal line shows how the Rebounder responds to the down-movement of bouncing. The horizontal line itself represents the Rebounder mat without bouncing.

If you look carefully, you see that all lines besides the red line have the exact upper and lower amptitude (or arch). What you see when you look at the red line is that the up-movement shows an arch while the down-movement shows a "bump". That means if you bounce on this kind of Rebounder, you will move up during the up movement, but during the down movement the mat does not give. Instead the mat stops the movement and you receive a jolt in your back. This is how a "bad" Rebounder works. The reason why the mat does not "give" are cheap springs and non quality mat material.

Only use a Rebounder where the upper and lower bouncing amptitudes are identical in size and shape. This assures that the mat cushions you as you approach the deepest point of your bounce, protecting your back from any jolting or jarring