There are several types of HDPE. The "softest" and the one I prefer, is the black HDPE 500. "Easy" to work with, virtualy unbreakable and the lightest of the bunch. The white HDPE 1000 is a tad harder, a tad more brittle- not saying it is anything but resilient- and is less easy to weld. Top End of the HDPE line atm is Dyneema. Yep, that too is HDPE, but you will find that only in line or weave.

Chopping board , if HDPE, need a tad more hardness, and is probably the cheapest one they can make with the chemical properties of HDPE, but also with a reasonable hardness to avoid fast wear when used for that purpose. Toughness is not even close to the wishing list of the producers.