The issue is there are two specs of certified padding.
The first is like pipe lagging, its round, wrap around and soft and its designed to stop you banging your knee or head climbing in and out of the car, it WILL NOT protect your head in a crash.
The other kind is a hard material which either looks like rubber or has a grain like polystyrene and is glued to one side of the roll bar tube and its designed to prevent point loading your helmet shell and reduce the decelleration of your head on impact. It's energy absorbing, but because its about a inch thick, and has to absord the energy of your head and helmet in a crash, its pretty solid at
@harvsurrey says and without a helmet isnt going to help you much.
@DaveDreads the difference is a) the harnesses (see earlier comments about a complete safety system) and b) that its not for competition. If you have the standard three point belt you need the airbag.
Once again, actual competition cars with all the safety kit, fine. Some chav in a corsa with cobra monacos, standard belts and a non airbag wheel isnt.