fiberglass, or you can install foam insulation on the underside of the roofdeck, one time, and never replace it again. Adding additional blown insulation or fiberglass will have a limited affect on your utility bill because, although it will do a marginal job of protecting your home from the heat in the attic, it does nothing to protect the duct work in the attic which can be exposed to up 200 degrees in the summertime. Foam insulation on the underside of the roofdeck will drop that temperature in the attic down to between 75 and 85 degrees. The advantage to that is a drastic drop in your utility bill over the life of the home versus a small reduction in your utility bill with blown in or fiberglass that needs to be replaced every 6 to 10 years. According to most cellulose packages, they recommend removing old insulation before installing new insulation . Cellulose over time loses its fire retardant features and becomes a fire hazard. Many companies that install blown in insulation in most cases will not remove the old, worn out, flammable insulation. They will just blow new insulation over the top of old insulation, trapping altered, pollutants, animal feces, you name it under your new insulation. If you want to research foam, go to building science.com and look under retro-fit, high energy homes. This is an independent source, not in the foam industry and once you study this website, you will be convinced that foam insulation can outperform all other insulations, hands down. Foam works year round, doesn't deteriorate, never needs replacing, improves indoor air quality, is pest resistant, and depending upon what foam you choose, can even protect your home from hurricanes. If you would like additional information, feel free to contact Doug at 352-874-6540, or e-mail: doug.thermasealcf.@gmail.com, or visit us at the Orlando Home Show coming up next weekend.