Insulation and STC Ratings for Soundproofing

STC stands for Sound Transmission Class — a rating of how well a material or assembly blocks airborne sound. The higher the STC number, the more sound it stops. It's the acoustic equivalent of R-value for thermal performance.

If you've ever wondered why some walls let every conversation through while others feel soundproof, STC is the measure behind that difference.

Insulation in a wall or floor cavity absorbs sound energy that would otherwise pass straight through the empty space, raising the assembly's STC rating. Denser materials like cellulose and mineral wool tend to dampen sound better than light fiberglass, though all insulation helps compared to an empty cavity.

So the insulation you add for energy savings also quietly improves the acoustics of your home — a welcome bonus.

Insulation for sound control is especially valuable between floors, in shared walls, around home offices and bedrooms, and in media rooms. It reduces the noise that travels between rooms and from outside.

It's worth noting that insulation is only one part of soundproofing — gaps, doors, and the wall structure all matter — but adding insulation is one of the simplest ways to make a room quieter.

The good news is you rarely have to choose between energy efficiency and quiet — most insulation upgrades improve both at once. If sound is a priority, denser materials and attention to sealing gaps push the STC higher.

A professional can recommend materials and details that hit your comfort, energy, and acoustic goals together.