Quick question re. absorption materials (Roxul)...

I have access to Roxul RHF-40 but I can only get the 2" product. It is the same price if I get 2@2" or 1@4". So my quesion is, would 2 pieces of 2" product have the same absorption properties of 1 piece of 4"? The specs of the 4" 4lb product look very good, but the 2" 4lb is very different, but I'm guessing that the absorption properties would be exponential the thicker it is. Thanks!!

Same thickness, same result - I'm gonna assume the main diff is in the lower 2-3 octaves? This is what the extra thickness gets you. Spacing the whole thing away from hard boundaries helps the low end absorption also... Steve