A sex pillow or Liberator (sex furniture) is a soft implement used to enhance sexual intercourse. An ordinary (typically firm, since soft pillows have a shock absorbing effect) pillow can be used. But there are also specially-designed sex pillows. Some even have 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 positions, some of which might be difficult or uncomfortable without it. A pillow can be used to provide support when one partner has back pain. A very common use of a sex pillow is to place it under the woman's buttocks or hips before assuming the missionary position; this pivots the pelvis and increases depth of pentration.