Soundproof interior door: fiberfill or foam?

[mstrand]

We have a soundproof door between the living room and bedroom. The frame is installed. Should I put insulation between the frame and interior wall, or should some kind of foam be used? If so, what kind of foam?

 

[Viktor Cz.]

Frames supplemented with soft sealant.

 

[Östlund]

Backing rod supplemented with sealant.

I would also go for that if I want it tight and quiet.

Keep in mind not to press in too much backing rod so that it becomes completely full.
Add backing rod from both sides and apply a sound sealant inside the room.
A tip is to press in the backing strip folded in half, or how to explain it. That way, it expands against both the frame and the doorpost

 

[mstrand]

Thank you for the help!