The last time I did any cutting of insulation, I used my Bark River Tusk... which is their fine A2 IIRC. It did a great job, even after if felt dull. Sharpened up quite easily too. But... if I had to do it again, likely to use a basic utility box cutter with the replaceable blades.
No, no. If you shoot Mongo, you'll just make him mad.
"Savages tear. Civilized people develop and use tools." - ElectricZombie
God bless John Moses Browning.
"Love and a .45 are all you need to get through the night. One will kill you, one will keep you alive. Love and a .45"