Hello all and thank you for existing. This is a great forum.
I made twelve panels using OC703. Shipping is a budget killer with OC703. Locally I can source Johns Manville TempControl R-15 Mineral Wool semi-rigid batt in [3.5" X 24" X 48"] that comes in a pack of 7 panels for $48 and no shipping cost.
I can not find any technical details for this material regarding Sound Absorption Coefficients. Does anyone know if this material will be comparable to OC703?
It's fluffy so it's different. Roughly, 1' of fluffy is 4" of rigid. If I were you, I'd cut the batts into squares and stack them with a wire support because it'll compress if you stack them directly. This is how I made my super chunks and out of the same material.
I guess it's down to semantics. The technical term is probably 'semi-rigid' in that it has a batt form and isn't exactly like cotton candy. As far as I know, you don't get 'rigidity' metrics but density in lb/ft3. I'm not sure where fluffy lies but it's less than 1.5 lb/ft3.
If you want something like panels then you need rockwool or OC 70X.