Duck Hold-It carpet tape is the best and it works really, really well. You can get a sample from the Hip Girl store to try it out: http://www.hipgirlclips.com/store/in...oducts_id=5713
. It has a self adhesive on one side and the grip is on the other. I wouldn't really call it a foam, actually I don't know what to call it. It's thin enough to allow your clip to close and it looks neat, clean, and professional.
Here is a video demo of how it works and looks: http://www.hipgirlclips.com/store/in...oducts_id=4878
I got mine at Walmart for $8.97 for a huge roll that lasts a long time, for me anyway. I think you can get it at Home Depot and Lowes, as well.
Hope this helps!