3/4” thick MDF - readily available at HD or Lowe’s. I put my Journeyman on the rolling stand and because of the weight, had to screw in every screw from underneath the table. My impact driver didn’t work with the provided screws so I did a pilot hole in each one and it took me a while to get all of the MDF slats in.
Now because I don’t want to replace the original MDF slats again, I plan to put another piece of MDF wasteboard on top of the original to use as my wasteboard. Shouldn’t be an issue with my Z as I’m a beginner and am doing basic projects now