Here is a great diagram of all the possible types of insulation, their R value and their environmental impacts. As green builders in Brooklyn we have specific needs. Doing a green renovation in a Brooklyn brownstone requires sound proofing in the walls and ceilings and lots of insulation that takes up little space on the exterior walls and roof.
My favorite is cellulose and salvaged PolyISO for these two needs.
Cellulose is great at soundproofing as well as being insulation. In the ceilings where you have a little more room you can put cellulose. It is recycled and has a million times better environmental impact than fiberglass which is also a good soundproofer.
In the exterior walls of the space craved Brownstone I like salvaged PolyISO. It is the highest R value per inch out of the insulation. On the exterior walls we are pretty fanatical about insulation – at least R 36 – and we can do that with only 6 inches of insulation. When we can we go up to 7.5 inches and get a whopping R 45. For the same reason we use PolyISO in the roof wheresound is not the issue and you just want to pack the R value is. There we try to go to R 90 with 10 inches.
And since the PolyISO is salvaged it is definitely the greenest choice in insulation.
On all the exterior walls and roof we also use reflective aluminium as a radiant barrier. You need to give it at least 1/3 inch of space to work. It is placed on the inside of the house near the sheet rock since Brooklyn is not a hot climate. If it were then the barrier would be on the outside. This has to do with where condensation collects. We use non-perforated aluminium taped well at the seams so it also acts as a vapor and air barrier.