I've been asked several times to describe tileboard.  It's a generic term for a material commonly used as a wall covering in damp areas.  It usually has a tile pattern embossed and printed on the surface.  The material I use is finished with a smooth white surface.  There are two variations of this product - a low grade product made with fiber board that's often used for dry erase marker boards and a much higher grade (and heavier) variety made from tempered hard board.  The fiber board product has a textured back which is not water resistant.  The tempered hard board has a smooth hard back and is very water resistant.  This is the variety that I use.  Like all wood based products it can be damaged by prolonged exposure to water, but normal painting moisture (even wet on wet) will not damage it.  Painting boards should be put up to dry so that no moisture is trapped between the board and your table.  The drying rack serves this purpose. 

Here's a link into the manufacture's web site.  I use the Thrifty White (300) for painting boards. 

Note: The white surface of some painting boards may contain minor manufacturing defects from the original material.  Nothing more than minor specks or pin-pricks.  This is normal for this material and will have no effect on usage.  Also, the back of some painting boards may have the manufacturer's label and/or splatters of the front surface paint.