Wall Insulation Retrofit (Drill & Fill) Insulate exterior walls with dense packed, blown-in cellulose.Insulate interior walls to help with soundproofing.We use cellulose as it performs better than fiberglass, yielding higher r-value, air sealing, and better soundproofing. It’s also fire-resistant. This application allows you to insulate without tearing down your siding or drywall.We can patch certain types of stucco as well as drywall.