Suspension protection refers to the padding system built into an instrument case that provides protection against trauma by absorbing the shock into the padding of the case.
Instrument Case Suspension
There are various designs available. Below is one example of a suspension case. Notice there are 3 points of padding, allowing the instrument to be completely suspended in the center of the case. For superior protection, the back of the instrument and the bridge should not touch the wall of the case the case.
The green case is an example of a non-suspension case. There is no padding to suspend the instrument, and when placed in the case, the back of the instrument rests directly on the wall of the case. Many times, these types of cases are made out of foam. If you were to sit or jump on the case, the case may collapse and your instrument might end up looking like the example below.