Printing with HDPE plastic Just out of curiosity is it possible to print with HDPE? 

Would it be easy or hard? 

I know they don't make HDPE filament* but I know people with a filament extruder could make some HDPE because it is a common plastic, which means it can be given a second use or something.

*To my knowledge
It can be done, although PE is not the best material to 3D print, as it has very low melting point (HDPE is just over 100°C), it is unpleasantly waxy to the touch and needs specialised paints and glues.

I never tried myself, but I know the RecycleBot is supposed to be able to use PE waste to produce a filament.