for vibrations yes. here is an example.
i have a crew cab truck, and the back cab wall was vibrating like crazy when i added subs. so bad that i could hear it over the subs.
i put CLD tile, on the left side, and it stopped ALL inside audible vibrations. now yes the cab wall still vibrates, and outside u can still hear it, but not on the inside. all i would have to do is put 1 more on the right side of the cab and it would probably stop 100% of the vibrations.
now a trunk, u prob could put 4 on say the trunk lid, and that lid wont vibrate. they are cheap though, u buy 10 of them and they are only $2.50 each. best $2.50 i spent to kill all my vibrations due to sub(on the inside of the truck, thats all i care about). i have cut up a few and put in my doors for my mids since i bought 10 of them.
gonna try his MLV for my doors to seal the big holes up and hopefully get more sound inside. im confident it will work