Got a question regarding HDPE, I'm using a 5mm thick HDPE baseplate for the build, but the material I got is warped and now I'm not sure if I want to use it any more. Is it normal for HDPE to be like that as even a couple of solid rods (30mm and 40mm dia) were bent?

I'm tempted to replace HDPE with an aluminium base plate but that will double the weight