Thanks, RUR. I stumbled across that same thread earlier this morning trying to find an answer to Markus' question. I'm not comfortable using the Rockboard information because, as Andre points out, manufacturer to manufacturer, and even region to region differences can be significant.
I've sent an email off to Roxul asking for the airflow resistance and resistivity. Let's see if they get back to me with anything useful, and in a timely manner. If not, I'll do what Markus suggested - stick it in the corner, and measure.