A sex pillow is a specially-designed and typically firm pillow used to enhance sexual intercourse. An ordinary firm pillow, however, may be used in place of a special one. Some contain a high-density urethane core to balance firm support with softness. In addition to more common pillow shapes, there are wedge-shaped, ramp-shaped, prism-shaped, etc. pillows which lend themselves to various sexual positions, some of which might be difficult or uncomfortable without them.