Response surface designs are types of Experimental Design that investigate the curvature of the response surface. They achieve this by using a quadratic regression equation rather than the linear form of the regression equation used in factorial designs.
When the response surface is approximated by a linear equation the maximum and minimum values always occur at a corner point. Thus it is not possible to use the regression equation to optimize the process if the true maximum or minimum lies within the interior of the response surface.
There are various types of response surface design including the Central Composite (CCD) and Box Behnken designs.