When it comes to cavity insulation, an energy-conscious builder has a lot of products to pick from and a lot of conflicting information to consider. In the running public-relations brawl between cellulose and fiberglass manufacturers, talking down the other guy's product has become a common marketing strategy. Even after you sort through competing claims for fire resistance, health effects, and "green" benefits (see "Marketplace Madness"), you still have to evaluate claims about cost and performance. In this article, we'll take a look at the realworld conditions that affect the performance of fiberglass and cellulose insulation, and give some tips for using each of them effectively. Of Price and Performance Many builders ignore the competing claims about performance and just buy the