I purchased the 48X36 inch rectangle and it is really good.  Make sure you measure the area you want covered first so you will get the correct size as there are a few sizes and shapes.  I have this on a low pile but squishy carpet and this does the job.  I was most pleased that I didn't stub a toe on it as I forgot I have it down.  It is very thin material with little spikes on the back that hold it in place.  So far so good!