A dual density NBR rubber pad shaped to support the back posture when used in the harness.
The pad has a soft layer, worn next to the body, and a harder dense layer which attaches to the harness with additional support from glass fiber battens sandwiched between the 2 layers, making it more comfortable.
The NBR Rubber moulds well to your back and has a small amount of shock absobtion without absorbing a lot of water.