Sturdy.
This is a very good mat, and worth the investment. I could tell the difference in my newly purchased rug that it gave it a more cushioned feel. It is very heavy, and feels even heavier as it grabs the floor and sticks to it while you are trying to arrange it in the best position. One thing I did:
Before laying your rug on top of it:
Get on hands and knees, and slowly spread out all the little folds and wrinkles until it is lying flat.
When lying your rug:
My rug is a 6 x 9. If your rug is smaller than the rug pad as mine is, I suggest lying it over one corner of the mat. This way, you have a straight edge to line it up, and you are cutting the mat from the other two sides. With the additional mat that I have leftover, I have stored it and plan to use it underneath a carpet runner one day!
One more tidbit: Once it has been laid, it is not going anywhere. I left a little bit to be seen (as I was alone in doing this) and it is a hard job to re-position your rug (again, because of the gripping effect of the rug pad). That said, if you have a willing helper, take it!