Wheelchair Accessories - 24" x 18" Medline Visco Form Wheelchair Cushion: 24" x 18" The Visco Form uses three different foam layers including high resiliency foam and a 4 lb. visco elastic memory foam. The base layer's dense foam provides structure and support, preventing the user from bottoming out. Visco layer is sandwiched between the HR foam. When the user sits on this cushion the visco elastic foam molds to their exact anatomical contour. This provides both maximum seating surface area for reducing high pressure zones and substantial contour to properly position the user.