Valerie writes from Boston, Massachusetts: "I understand that compressing insulation reduces the R value from the perspective of heat loss. But how about sound? If I use a thicker batting and squeeze it down will I get better sound reduction?

I will be using it in 2x4 wall studs that separate my condo from the neighbors. Should I therefore get 3 1/2" or can I use thicker that is compressed. And does the R value matter for sound?

I would use the QuietZone® add generic but my local retail outlet doesn't have it and I don't have time to order it."

Answer: You are correct; compressing fiberglass insulation does reduce the R value. However, R-value is a measure of thermal performance, not noise control. The rating for sound is STC or Sound Transmission Class, a quantifier used to rate walls, doors and windows for their effectiveness in blocking sound. STC ratings are based on testing the whole wall and the higher the STC rating, the more acoustic value the wall has. Since the 2X4 wall you want to insulate is essentially an interior wall between two condos, we recommend using a 3-1/2" insulation product, either standard R-13 or higher density R-15.