AliMed® T-Foam™ Cushion with Solid Seat Insert™ A firm convex base fills the wheelchair sling seat and creates a flat sitting surface. Cushion combines T-Foam with a Solid Seat Insert, creating a flat sitting surface. Optimal pressure distribution with minimal change in seated height. To determine overall cushion thickness, add 1-1/2" to the thickness of foam selected. Black, breathable polyester knit cover with non-slip vinyl. Choose between Soft or Medium foam.