[bpape]

Just for some clarification...

The acoustical cotton is in fact fire rated - and class A at that.

Also, there are 3lb and 6lb densities available in 2'x4' sheets - 1" and 2".

The 3lb cotton is in fact more expensive than the 703 - about double. Now, for that cost, you gain not HAVING to cover it, no itch or hassle installing it, and it comes in your choice of 8 colors. Not for everyone but something to consider when looking at costs.

Lastly, to the original question, if you want to save some $$$, you can do 6" of 703 for 75% of the cost of 4" of 705. It will work just as well if not better due to the additional thickness. Mineral wool will be cheaper than either of those solutions - but harder to work with.

All depends on what you're looking for.

Bryan