They are aluminum, with a gritty, non-skid backing (sorta like the sandpaper I back my own templates with). There is a 1/2" seam allowance included. The blunted edges are very helpful, too. When the pieces are placed right sides together, all the edges match (no "dog ear" triangles to deal with).
I can hardly wait to cut me some fabric with these babies!! Oh, yes, I can use my rotary cutter with 'em!!