OK Bosal makes 3 kinds of interfacing foam. One that has adhesive on one side, one that has adhesive on 2 sides & one that has adhesive on no sides (sew in). If you have the single sided variety, you should be able to tell the difference. If you have one of the other 2 varieties, both sides are going to look the same. If you can't tell, just snip off a sliver & do a test on a scrap piece of fabric.