The batting that I used..
was the "unfaced" batts.....if you are adding more insulation (like I am) over existing insulation, you want to use unfaced. Faced ("kraft") batting placed over the top of exsisting insulation can trap moisture..a big no-no.
I used home depot model #396063...R-30 unfaced 15 inch, 25 ft x 9.5 inch continuous roll. 31.25 sq ft. $9.37
But still take in the Lowe's ad for 30% off if you want any type of insulation.