I didn't specifically notice the difference when I added it but yeah my van is super loud on the freeway. Hard to have a conversation
and I have to crank the radio. I browsed the thread(s?) about covering the floor and side panels with that silver stuff but am not convinced it's worth the trouble (?) since my carpet is short & gray; not shag, looks good enough, and is the least of my concerns. Perhaps worth looking at something for the pop-top though.
I used spray foam to fill & fix a number of things in the pop-top retrofit/repair including fill for fiberglass. One thing was the wood curb on the ceiling had been beat up & pulled from the fiberglass shell, but it was hard to reach & fix without a total tear-down. There's a sheet of thin plywood which is probably glued to the FG shell and that is stapled to the curb before gluing. The FG has recessed grooves a few inches wide for stiffening on the top surface:
and the thin plywood is presumably glued to it at the low points. This connection was all broken up in the front from pulling up by the wind. So I drilled holes & filled some of the gaps with the expanding spray foam stuff. Nasty chemical sprays & all but it seemed to work well & make sense. A technical problem is the spray can didn't seem to be putting out much when squirting vertically, when it became less than full, or maybe after a few seconds even when fresh. The stuff expands over the next quarter-hour or so as it cures and I could tell where it was working when it oozed out the sides. Be ready to scoop up the sticky ooze as it plops down onto the sides of the van. That stuff dries firm and is best trimmed the next day when it's stiff, using a sharp, long utility knife blade.
Maybe shag carpeting is good for sound control. Or some kind of egg crate soft textured surface on the ceiling. It would be really nice to have less road noise. Perhaps the floor insulation is the best route though, since simply deadening internal noise with an egg crate ceiling means I still have to yell to the passenger & turn up the radio. The floor is already under a compartmented deck though so I'm still not sure that's the most important source of noise. It could well be the pop top making it so noisy. I usually have the driver's side window cracked too which is definitely very noisy!