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The Best Blown-In Insulation for Soundproofing
It is a question we are asked all the time, so here is the honest answer. When it comes to the best blown-in insulation for soundproofing, from a purely soundproofing point of view, we cannot really recommend cavity wall insulation at all. In fact, we have yet to see a property with blown-in cavity insulation that does not also have a noise problem.
That surprises people, because insulation is meant to help. The reality is more complicated, and it is worth understanding before you spend money filling your walls, which is exactly the kind of honest guidance Quietco is here to give.
Why It Can Make Noise Worse
The problem is what happens to the cavity’s air gap. Polystyrene bead insulation, and injected or spray foam, fill that gap, and sound actually travels more easily through foam and beads than it does through air. In other words, filling the cavity bridges a gap that was quietly helping to hold noise back.
The result is that homes which have had beads or foam injected tend to suffer more from impact noise, footfall, furniture being dragged, doors banging. It is a known limit of insulation in general. As the building science site Energy Vanguard explains, insulation absorbs some sound, but it does not add the mass or the decoupling that actually stop the toughest, lowest frequency noise.
What It Means for Your Property
The effect depends on the kind of home you have, but it is rarely the improvement people hope for:
- In a detached property, you can suddenly start hearing things you never noticed before, footfall, children playing outside, and environmental noise like aircraft and road traffic finding its way in.
- In semi-detached and terraced homes, you are more likely to hear impact noise travelling through the structure from noisy neighbours.
Either way, filling the cavity has made the wall a better path for sound, not a worse one. That is the opposite of what most homeowners are hoping to achieve.
Is Acoustic Mineral Wool Any Better?
If something has to be blown in, then acoustic mineral wool is the least problematic option, because it is absorbent rather than a rigid bridge across the cavity. So if you are choosing purely between blown-in products, that is the one we would point to.
There is still a catch, though. Having looked at many homes across the UK with a thermal imaging camera, including our own, we know that blown-in insulation never quite reaches every corner of a cavity. It leaves pockets that were simply never filled, which makes it unreliable as a way of controlling noise.
The More Effective Approach
This is the heart of it. Rather than trying to fill a cavity you cannot fully control, it is far more effective to install a proper soundproofing solution on the inside of the property. That way you reach many more of the paths the noise is actually taking, whatever kind of home you have.
Detached, semi-detached or terraced, treating the noise from the inside gives you control that blown-in insulation simply cannot. You can read more about how we work and why this approach delivers.
Fill out the contact form to book your FREE noise diagnosis call and find out the best way to quieten your home. Get in touch here.
Quieter and Warmer
Here is the part that often gets missed. Soundproofing is not only about noise, it is genuinely effective thermally too. When we add sound insulation to your walls, ceilings and floors, we are also reflecting heat back into the room and helping to keep it in.
So a proper internal soundproofing solution gives you two things at once: a much quieter home, and a warmer, more energy efficient one. It is a far better return than filling a cavity and hoping for the best.
Frequently Asked Questions
What is the best blown in insulation for soundproofing?
If you must blow something in, acoustic mineral wool is the least problematic, because it absorbs sound rather than bridging the cavity. But it never fully fills the cavity, so treating the inside of the property is far more effective for noise.
Does cavity wall insulation reduce noise?
Usually not, and it can make things worse. Polystyrene beads and foam bridge the cavity air gap, and because sound passes through them more easily than through air, impact noise often becomes more pronounced.
Can spray foam make noise worse?
Yes. Whether it is foam in the loft or injected into the cavity walls, filling that air gap tends to leave homes suffering more with impact noise, not less.
Does soundproofing help with warmth too?
It does. Adding sound insulation to walls, ceilings and floors also reflects heat back into the room, so a good soundproofing solution makes your home warmer and more energy efficient as well as quieter.
