I bought some black esun petg the filament seems fine on the spool not brittle but all the prints are very brittle. Printing with a qidi x-one with temps at 240 head and 70 bed. Esun recommends 230 - 250 head no heat to 80 on the bed. I'm at my whits end trying to figure this out i'm thinking bad filament. What would cause this and could it be bad filament?