This is the one!  It actually is half an inch thick as described, has a nice rubbery underside, and cuts easily with kitchen scissors.  I put one of these under a rug that had simply REFUSED to lay flat even though I piled boxes of books on it and waited over 8 months, and VOILA! The rug is now flat.  It is just short of a miracle and I will bookmark this rug pad and always buy it from now on.