A 12% symetrical airfoil is the thinnest you can run without a loss of angle of attack/lift. There is really no advantage to going thicker for aerodynamics sake; butfor structural reasons, it can allow for a stronger wing with no weight penalty. In an Extra, you want to be able to stall the wing quickly and completely, so thats part of what your buying. This is assuming we are talking about NACA 4 digit airfoils.</p>