We recommend two layers to maximize noise reduction for a car door.
Your first layer is always
Damplifier Pro. It will demolish metal vibrations give any car door that solid, luxury feel.
Your second layer depends on the noise problem you want to solve.
OverKill Pro will decouple the plastic panel from the metal and eliminate those annoying plastic rattles.
Mega Zorbe will absorb sound inside the door cavity, cleaning up speaker sound and reducing overall noise from your door.
Luxury Liner Pro is used to seal up the door cavity, improving mid-bass and also quieting the door.