Hello Char. The thickest paper the ET-2850 can print on is Epson Ultra Premium Photo Paper Glossy which weighs 79 lb. (approx. 297 gsm). We have tested Epson Ultra Premium Presentation Paper Matte, which is the closest material to cardstock that works with the machine. However, that paper weighs around 44 lb. (approx. 165 gsm). You can always try cardstock that falls in between that range at your discretion, but please note that your results can vary when using 3rd party paper, as these recommendations are for Epson paper only. Regards, Kevin - The Epson Team.