This might sound a little crazy, but the "impact" to a horse's back while riding is actually quite low... we know this because we measured it. Many brands attempt to solve impact absorption with dense impact foams and plastics, but they are solving the wrong problem. This is because the PSI exerted over a horse's back is typically only in the 2-4 PSI range (which is low). For perspective, an adult will exert over 10 PSI on the ground while walking.
The data shows that the way to make a horse comfortable and protect against soreness is to dampen all the small movements under the saddle, similar to the shocks in your car that soak up all the imperfections in the road to make a smooth ride.
This is what the squish panels do. They dampen the movements to make for a more comfortable ride for horse and rider. This softening is very obvious for horses or riders with sensitive backs.