What's the BEST firewall insulation material?

Hi,

I have to install new sound absorbing material in the engine
compartment. My Mexibeetle doesn't have any installed.

What is the BEST firewall material available today? I can't imagine
that the old tarboard firewall stuff that was used 30 or 40 years ago
is still state of the art.

Found some stuff an JCWhitney. They offer rubber firewall insulation
kit and claim it is better than the old ones. Is it really? This is
the best stuff out there or anything that's better?

Thanks for your help,

Marco