Using acoustic panels is a good way to block off the noises coming from the outside.
Normally, such panels are used in recording studios as they’re good in improving the acoustics inside a room.
For your information, there are two kinds of soundproof panels:
- Foam Panels
- Fiberglass Panels
Though they are both panels, they have different effects on sound.
The first one helps reduce the echo in a room. If your purpose is to record sound inside a room, foam panels are what you use.
Fiberglass panels are effective in blocking the noise.
Therefore, since the goal is to soundproof interior doors, fiberglass panels are the ideal type of panel to use. Of course, you can use both to reduce the echo and block the sound.
You would need adhesives to install them at your door.