Roxul insulation is Ben Bogie's preferred insulation (especially on small jobs and when he's trying to create a really robust, hydric shell). Not only is it easy to cut and tuck into bays and just generally work with, it's also loaded insulatory advantages: good R-values, air sealing, and moisture management; it's inorganic, so no worries of mold or biological growth; and it's a strong fire retardant. It's not really surprisng that it's Bogie's go-to.