So far 10mm has held out fine in the featherweight class. be prepared though, some nasty spinners will get through or at least leave nasty gashes.

I disagree with Juha about putting metal in front of it, we did that on our raptor and that was the stuff that took the full force of Prolodja, where the HDPE alone would have just absorbed the blow and flexed the energy out.

It is also the way you use it that matters. Bolt HDPE straight to a steel frame with no possibility of flexing, and it will not be as effective as when you do suspend it in such a way that it can give way.