The FIA specified tests require a simulated human headform in crash helmet to impact at no greater than 300g. To achieve this requires special energy absorbing material but which does not protrude significantly into the cockpit of what is already a restricted space because of modern roll over protection systems.
The vast majority of FIA approved paddings achieve this with a thickness of just over 25mm and therefore have to be made from fairly rigid polymer type materials. The alternative would require around 75mm of softer material, such as Confor foam, so inevitably there is a compromise for the solution. You might consider the hardness of similarly rigid car dashboard material and which has to demonstrate similar energy test results.