Mike writes from Oxford, Michigan: "I have 12" (R-30) of CertainTeed's InsulSafe 4 Premium blown-in wool/fiberglass insulation (sorry, I know it is not your product). Anyhow, I am looking to upgrade to R-49 (18") and considering your blown-in fiberglass insulation (through The Home Depot). Every article I have read on the internet so far says that blown-in fiberglass doesn't compare to cellulose for maintaining R-value at extreme cold temperatures, and in conditions with convection (i.e. windy areas & attics). I would like your honest, expert opinion."

Answer: Attached is a bulletin developed by Owens Corning that compares fiberglass insulation with cellulose insulation. In a nutshell, tests have shown that fiber glass loosefill products actually experience better thermal performance as the temperature in an attic drops, but that some light-density fiberglass loosefill products may experience a reduction in thermal performance as the temperature further decreases. However, the impact of this on annual utility bills is insignificant. In my view, a bigger concern is the risk of reduced R-value through settling with cellulose. Your call, but you know my preference for PINK insulation.