The heat insulation part works pretty good depending on the products used.
The heat of the hood is much less with insulation, but it only provides a few extra seconds protection if there is a carb fire.
Concerning sound isolation....welll, not so much.
Technically yes there is come sound abatement because the insulation will absorb some sound waves, especially higher frequency waves.
But the overall sound, especially inside the car, is basically unchanged.
This is because the low frequency waves permeate the car through the large sheet metal areas that turn into resonators of a sort.
Unless you can literally dampen the metal of the hood you will not decrease the sound coming through the hood by much.
Also, don't forget about the opening of the grill and the gap all the way around the hood to fenders.....there are just too many areas of sound release to make much use of sound deadening under the hood......but it is still used because every decible counts in overall testing terms.
