What is the best brand/product for maximum acoustic performance for insulation between 2x4 400mm studs and joists? I'm looking at all sorts and it's starting to get a bit confusing as so many difference varieties: slab, rolls, densities, rigid on one side, loft, cavity, etc. I've seen on some threads that people say it doesn't really matter and you can stick loft insulation in-between the studs?   I'm thinking 100mm everywhere. just cram it in all over the place. But som