Posey Wedge Gel Foam Cushions gently rotate the hips back to help prevent forward sliding. Wedge shape is also an aid to "foot propellers" and an effective restraint alternative against the hazards of unassisted wheelchair exit. Use flat bottoms for wheelchairs equipped with a Posey semi-rigid foundation, drop seat or other uses. Convex bottom cushions are ideal for use in standard sling wheelchairs to reduce the "hammocking" effect.