Coccyx cutout extends from back of cushion all the way to the center oval cutout. This provides complete comfort for sore areas and also helps improve airflow so user is cool and comfortable Wedge shaped cushion features tapered design – thicker in back and narrower in front. This allows complete support where you need it (tailbone, buttocks) and less support under thighs. Especially helpful when driving or sitting at a desk. This design also helps circulation under thighs. Ergonomic design helps promote proper posture by slightly tilting the pelvis forward. This maintains the spine’s proper lumbar curve for low back comfort and pelvic support. Constructed of one-piece molded support foam – designed to provide optimum support while remaining comfortable. Cushion is 17 inches wide x 16 inches deep x 5 inches ( at the highest point for tailbone).