I have a room made of hollowed concrete blocks that I framed by mounting 2x4s, wide side against the wall. This gives me a 1.5in depth cavity to fill with insulation.
Should I use an r19 fiberglass insulation and compress it down from 6" to 1.5"? Or should I use a 1" foam board (r5)? I know compressing insulation lowers the r value. I'd like to get the r value as high as possible (recommended is r13 in Florida)