MDF boards are made of wood fibers bonded by synthetic resin and compressed through pressure and heat, resulting in a solid and very uniform board with good finish and durability. Because the fibers are randomly oriented, the machine can cut them in any direction, delivering a smooth surface to the touch. Naturally, the board does not resist water well, but there do exist options on the market that are more resistant to moisture and sometimes even fire. http://www.hengyuwooden.com/fitness/fitness-equipment/