What kind of mat do you use for running Mindstorm EV3?
Mats are sometimes used with Mindstorms to create line following bots or for defining more complex tasks.

I can't give great advice on printing a mat for EV3, as I've never done this, but I would imagine that you'd want to be able to print on a large, fairly stiff piece of paper or cardboard. If you're just trying to create a basic line for your robot to follow, you can use a piece of posterboard and then add a line with black tape, markers, paint, etc.

There are several different mats that LEGO has made available for Mindstorms over the years:

https://www.bricklink.com/catalogList.asp?pg=1&amp;catString=246&amp;catType=P&amp;v=1

I believe the most recent is actually the box sleeve in the EV3 kit:



You might want to just purchase one of the officially released mats.