The best replacement for fiberglass insulation is cellulose.

The best alternatives to fiberglass insulation are rated as following:
★★★★★  cellulose
★★★★★  foam
★★★★  spray foam
★★★  cellulose insulation
★★  mineral wool
★★  foam insulation
★★  foam board
★★  styrofoam
★★  roxul
★  denim
★  radiant barrier
★  blown in
★  stone wool
  rockwool
  spray foam insulation
  rigid foam
  foam board insulation
  green fiber
  icynene
  closed cell spray foam
  mineral fiber insulation
  polystyrene
  foil insulation

Your alternative for fiberglass insulation is not listed? Suggest!
Speaking about fiberglass insulation, one probably shouldn't forget about vapor barrier.

Other search terms related to fiberglass insulation and their ratings are:
★★★★★ vapor barrier
★★ radiant barrier
You have in mind a companion for fiberglass insulation and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fiberglass insulation in all years. Click on graph for more.
fiberglass insulation
cellulose
foam