[a1a]

Did some quick research out of interest. Melamine and porcelain steel seems to be the most common.

References:

http://mywhiteboards.blogspot.se/2012/06/melamine-vs-porcela...

http://www.whiteboardsetc.com/laminated_panel.htm

http://dryeraseboard.com/aluminum-trim-porcelain-steel-marke...

http://www.usmarkerboard.com/s/Unframed-Whiteboard-Material/...