Spray Foam Insulation
Its definatly more than fiberglass batts but compared to everything else, solar electric, hydro geothermal, its the most bang for the buck. Open cell stops the air flow and seals any thing, at the same time its relativly inexpensive compared to filling the cavity. The blowin blanket is not much more than batts and way better, the ridged at 1/2 thick can be picked up between 8 and 12 bucks a sheet. I did the blow in and ridgid on mine. I thought that the ridgid also take care of pass thru air which it does but it doesnt take care of the internal wal air flow. Im not sure on my next house if I would use the spray or not. Definatly would put on the ridgid. You can see the difference in my house in the winter. Most houses you can see everystud line on a frosty day. On mine no such thing. Its also sealed the gaps around end of sheets and exteior penetrations.