Fiberglass batts were the most commonly used and widely available insulation type in Phoenix.  Often itchy and an irritant, fiberglass insulation is not a material you want to handle for a long time.  The R-value of fiberglass is highly dependent on how it was installed.  To achieve the best R-value, the batts should be in continuous contact with the drywall and cut exactly to length.  However, all too often we find they are too long, bunched up, thrown on top of recessed canned lights, falling off or simply laying on top of the studs which reduces the R-value and creates air pockets that can increase convection and heat gain into the home.