My Dad used to use thin material & glue a stiffener on the under side.
I used 1/2" thick material & rabbeted the edges all the way around & ran a groove where the blade went through the same depth as the edges. This gave clearance for the ZCI to set fully down into the table before the blade was rolled up through it. I have used good quality plywood as well as cutting board material I got at Ace Hardware I made several ZCI out of that material it cost around $3 per ZCI.
"Forget the flat stuff slap something on the spinny thing and lets go, we're burning daylight" Bart Leetch
"If it ain't round you may be a knuckle dragger""Turners drag their nuckles too, they just do it at a higher RPM"Bart