Fiberglass is an insulation material composed mainly of glass ... This heat resistance is measured by the R-value, which ranges from R11 to R19 for walls and can go as high as R30 for ceilings ...

For example, homeowners in parts of the southern United States can insulate their attics with materials that have R-values in the R30 to R60 range and R13 to R19 for floors. Meanwhile, people ...