Abstract: Panels comprising first and second layers and a core disposed there between, wherein the core has a plurality of walls providing a series of connected cells, wherein some of the cell walls have openings providing fluid communication between a series of at least 3 cells, and wherein the opening in a cell wall has an area that is at least 50 percent of the area of a side of that cell wall. Exemplary embodiments of panels described herein can be formed articles such as panels, walls, or other parts with curved surfaces. In one exemplary method, panels are shaped via thermoforming. In another exemplary method, panels are shaped via insert molding to provide the article. In another exemplary method, panels are shaped via compression molding to provide the article. The panels are useful for absorbing sound in a designed frequency range.