For some reason you can't just buy these clips seperately from IKEA, and even if you if you could they'd be overpriced as f… just like every piece of powder coated metal this tax-avoiding illegal-lumberjack-ass company sells…. 

Anyways, enjoy your free clips! Material doesn't really matter as long as it just has a little bit of flex, printed with 4 walls at 0.3mm layer height in strength profile on a P1P