This is from the Kickstarter that Games and Gears did a while back and had a lot of trouble with (Battle Boards). It took a long time to get it and I paid $150.
They don't appear to offer them anymore on their website.
It is plastic with supports underneath and about an inch thick. Very light though - once all 6 are connected I can pick up and flip the whole thing. It's not heavy, just awkward at that size.