frarose,
I think it's Pellon 987 fusible fleece. It's called for in the Bow Tucks purse pattern. I've used it in the bow tucks i've made. It's a pretty lite-weight "batting" and gives a little body to the purse.
It's availabe at most of the fabric stores. I usually get it at Hobby Lobby when they have a 40% off coupon.