With sound deadening it goes like this,
butyl is better than asphault,
thicker IS better (the reason why some people take a choice sound deadener and do TWO layers, you might ask, Why two layers? When you add that second layer it works with the first layer tripling its sound deadening properties)
BUT remember with thickness there is WEIGHT, The Damplifier pro is the thickest out on the market currently hands down. I ordered 160 sq ft. of this stuff, the box weighed in at 95 LBS.!!
Some of you racers out there try to reduce weight, remember, the more liners, deadeners, rattle pads you add the more weight you are adding to the ride.
My purpose of deadening my ride is for a sound system, I know that this being an over 30 year old car, they didnt have the technology they do nowadays with bass/amplifiers/4x50watt head units, so there is going to be alot of sound escaping or being drowned out by road noise. A sound deadener allows the freq. played within the car, to stay within the car.
Basically depending on if your going luxury car or race car you make the decision of what to use.
Race car- dont bother with this stuff!
Weekend Racer/Daily Driver- I would just get a sound deadener do a layer, you want a somewhat comfortable ride while keeping weight as low as possible(adds about 100 lbs with about 160 sg ft. of the heaviest/thickest stuff[damplifier pro])
Luxury car/Show car/Daily Driver- Buy as much of this stuff as possible! Fill every inch! Use two-three layers of a sound deadener, a heavy liner, a sludge deadener, firewall deadener, spray wheel wells with spray sound deadener.(This setup will add probably 300-400 lbs! But weight doesnt count in the name of luxury)
I explained the sound properties but any sound deadener will also provide as insulation(think of a drink cooler).