Any lightweight, fusibles interfacing is fine, brand isn't important. Not paperbacked fusible used for applique! ( like steam a seam, wonder under or heat n bond-- those are a totally different product) just a lightweight Interfacing. Joanne's & hobby lobby carry many to choose from- they are inexpensive ( kind of like a dryer sheet with fusible added to one side.) They remain on the back of the blocks--are not removed.