Lots of options and information online. I am using Rod Gervais 'Home Studio Recording' Build it like the Pros as my main reference and researching others' work online. My goal was to find the JM Linacoustics R300 as he suggests but it seems impossible to source. it depends on your region. Some other acoustically tested options I am looking at are: Knauf duct liner or Knauf ECOSE® Black Acoustical Board Manson Acoustik-R duct liner JM does not actually seem that superior, and