Thermal insulation resists heat transfer — measured in R-value — required in all exterior assemblies by building code. Acoustic insulation reduces sound transmission between spaces — measured by STC (Sound Transmission Class) — not required by code but increasingly specified in quality construction. Mineral wool batt serves both functions simultaneously: excellent thermal performance in exterior walls and meaningful acoustic separation in interior walls. Fiberglass batt provides strong thermal performance but modest acoustic benefit. Spray foam provides excellent thermal and air-sealing performance but limited acoustic benefit due to its rigid nature. RainFire Builders identifies which walls benefit from acoustic treatment and specifies the appropriate product for each location.