The OEMs used acoustical products to dampen harmonics. When vehicles are running down the road they create vibrations (harmonics) in all areas of the vehicle. Some harmonics are considered good but most are very bad. In some areas of the car the harmonics are more noticeable. When an OEM applies
a dampening product in a certain area you know that there is a reason for it so it's a good idea to replace the material when you are doing a restoration or upgrade. . You car and your body will thank you for it in the long run..
BTW - using solid seat mounts under a racing seat is not good for the kidneys if your running the vehicle for any length of time such as in street car applications..