Within an area of substantially regular hexagons arranged at regular intervals on an imaginary reference plane, a sheet material includes a concave-convex section (20) having a basic pattern in which one first region (A1) is surrounded by six second regions (A2). This basic pattern repeats in regular intervals in lateral and longitudinal directions of the sheet material. The concave-convex section includes first protruding portions (21) and second protruding portion (22), which protrude in opposite directions from each other in the thickness direction in the first regions and the second regions, respectively. The first and second protruding portions may have a hexagonal pyramidal shape or a truncated hexagonal pyramidal shape.