Yield strength is different than tensile strength. The yield is how far each spring will stretch when bouncing or just by standing on the mat. The multi purpose rebounders usually have a wider yield range while the rebounders dedicated for those that want to do rebounding for the Health Bounce will have a very short yield. The more the rebounder mat bottoms out to the floor, the more yield the spring has. The higher carbon springs should have a higher yield without losing its tensile strength. The Cellerciser is the best example of a high tensile strength high yield rebounder.
If the wrong rebounder is bought and one of the springs loses its yield strength, the entire set of springs must be changed, not just that one spring. Also, bungee rebounders need to have their cords replaced more than any spring rebounder.
The rebounder springs that have the lowest yield strength will usually start giving deeper bounces that bottom out the mat lower and lower until it becomes less responsive to the point my feet hit the floor. Deep bounces might feel super soft but this is not the point of rebounding. Jumping just to have more air time is not the purpose of rebounding. The bungee rebounder has the highest yield of any rebounder but this is only for cardio and toning if using weights and has virtually zero “pop” at the bottom of the bounce. It is a push motion rather a pop motion. It is nearly impossible to do the health bounce on a bungee rebounder. The whole purpose is to flush my lymph vessels when I jump.