My budget efforts in the home studio...of course Sonar equipped for recording the audio for the vid....  showing the popular fad of slathering *acoustical* fiberglass insulation all over the walls.  Actually, it works great...  better improvement than turning my monitors vertical!  But seriously, it was totally worth the effort.  Now to investigate ARC  ;-D

https://www.youtube.com/watch?v=eDeF4sbhS1M

fiberglass is not something i would recommend.
 

Fiberglass (and mineral wool) is a much better bang for the buck than foam. Although I've noticed that over the past 10 years the price of rigid (compressed) fiberglass has shot up by 50% or more. I guess Owens-Corning's market researchers figured out that home recording enthusiasts are willing to pay more than designers of walk-in refrigerators and heating ducts. Fortunately, Owens-Corning isn't the only manufacturer and there are alternatives.
 
 
 

If you're using fiberglass you might want to cover it with some fabric.

don't use fiberglass.
it is the wrong tool.
it will only attenuate highs, at the cost of square footage.

batsbrew
don't use fiberglass.
it is the wrong tool.
it will only attenuate highs, at the cost of square footage.

but there is so much credible information online to the contrary: http://ethanwiner.com/basstrap.html http://www.bobgolds.com/AbsorptionCoefficients.htm  http://www.gikacoustics.com/diy-acoustic-panel-frames/
 
Rocky

batsbrew
don't use fiberglass.
it is the wrong tool.
it will only attenuate highs, at the cost of square footage.

not entirely accurate.
 
Fibreglas and rockwool can provide a much more broadband (and even across that band) absorption than most closed cell foam products. There are, of course, exceptions on both sides of the fence.
 
But as a general rule there are no general rules<G>... you need to hit the books or hire the services of someone that has. This is not rocket science, but by the same token it is very easy to spend money you don't need to.