3 different foam layers including high resiliency visco foam Molds to the user?s exact anatomical contour Provides maximum seating surface area for reducing high pressure zones Substantial contour to properly position user Fluid proof, easy to clean cover 325 lb weight capacity Available in thefollowing sizes: 16" x 16" x 4" (41 x 41 x 10 cm), 18" x 16" x 4" (46.x 41 x 10 cm), 18" x 18" x 4" (46 x 46 x 10 cm) and 20" x 16" x 4" (51 x41 x 10 cm).