I'm renovating my apartment and I want to better insulate the walls facing the street because there's a lot of traffic noise coming in. I've seen options like mineral wool, expanded polystyrene, and polyurethane foam, but I'm not sure which one is most effective without losing a lot of interior space.
How much space can you actually sacrifice in those walls? Mineral wool is your best bet for noise because it absorbs traffic frequencies really well, though it does take up quite a bit of thickness. Expanded polystyrene is thinner but less effective acoustically, and polyurethane foam is expensive without being significantly better than wool for this specific problem. If space is critical, combine mineral wool (about 5 cm) with acoustic drywall; that gets you decent insulation without losing too much.
The thing is, effectiveness depends way more on how you install it than on the material itself. You can have the most expensive mineral wool on the market but if you leave gaps or don't compress it properly, it's basically not going to work. What a lot of people overlook is that you need an **air gap** between the insulation and the outer wall, even if it's just 2-3 cm. That really makes a difference for traffic noise, because sound bounces before it reaches the insulation.
Mineral wool is still the best noise-to-thickness ratio, honestly. With 5-7 cm you'll get rid of a decent amount of traffic noise. Expanded polystyrene is cheaper but absorbs low frequencies worse (the rumble from heavy trucks is still going to bother you). Polyurethane foam is pricey and takes up less space, but it's harder to install without professional help.
My trick that actually works: before you put the insulation in, line the wall with a layer of acoustic sealant or sealing tape in the cracks, corners, and where the electrical wiring passes through. Sounds dumb but sound sneaks through the tiny gaps. After that, the insulation will actually do its job, not just be sitting there taking up space.
It's not just the material, but the combination with what you put in front of it. If traffic noise really bothers you, mineral wool works well, but what makes the biggest difference is leaving an air gap between the wall and the insulation, or even better, adding acoustic panels or resilient drywall on top. Polyurethane expands more, so it takes up less thickness to achieve similar thermal insulation, but for low-frequency noise (like heavy traffic) you need more mass and absorption, not just density - that's where mineral wool wins. The reality is if you just stick mineral wool directly to the wall without that air gap, you're going to lose effectiveness.
Log into answer.
