4-inch CornerFill is a 4" x 4" x 24" section of flat-cut Studiofoam acoustic absorber that is beneficial in two ways. Aesthetically, it provides a smooth, clean edge against which to butt other acoustic wall treatments and acoustic foam bass traps for a more professional appearance. Size wise it is a terrific way to finish out 1" or 2" foam products. Acoustically, it smoothes out the excess low frequency energy that congregates in room corners.