Can you fill a hollow door to make it soundproof?

Yes, you can fill a hollow door with foam or insulation which would help in reducing the sound transfer but it will not make the door soundproof!

Three layers make up hollow-core doors: an air-filled honeycomb interior and two thin veneer or panel exteriors. The narrow solid space between those layers makes it easy for sound to pass through.

As the primary soundproofing option, you can raise the mass of your door as it increases the number of molecules at minimum that sound waves must pass through, resulting in more exertion of soundwave energy exertion and less transfer of noise. You may add mass to a door by doing a few things as specified below.

an image showing different layers of hollow core and solid core door
  • Insulation Spray foam: You can fill the door with spray foam to fill the cavity inside the door. You’ll need a few cans of insulation spray foam for this. Drill a few holes in the door, then spray the foam through those holes. Inside the door, the foam will expand and harden over time. Do not forget to wear gloves, as it’s tough to get them off if it sticks to your skin!
S.No.Hollow/Foam FilledNoise Transfer
1.Hollow Door50-52 db
2. Hollow Door filled with Foam49-51 db

As you can see from the results spray foam is not very effective at soundproofing, it would reduce a few db but it’s not worth it.

  • Acoustic Panels: The panels help in reducing the echo by absorbing sounds. A different approach for using acoustic panels would be installing them inside the hollow door. It would take effort and a lot of mechanical work, so I don’t recommend this if you’re not used to DIY projects.
  • MLV (Mass Loaded Vinyl) Barriers: MLV barriers, composed of salts, microscopic metal particles, and sand, are more environmentally benign than traditional soundproofing materials. MLV barriers are typically supported by drywall and plywood structures. They generally have three layers: two external foam layers that trap airborne noises and reduce reverberation and a core barrier that absorbs impact noises.

Also read: How to soundproof a door like a Pro?

Conclusion

So, can a hollow door be soundproofed? Absolutely. The strategy outlined above will help to lessen the majority of the sound that enters the entryway, and they will, however, always partially eliminate it.

This means you must approach the project with realistic expectations to be satisfied with the results. Soundproofing a door can be inexpensive or highly expensive, and it is up to you to determine which option is best for your environment and your budget.