Cutting Foam For Chair Cushions . The foam carving knife is helpful for jobs that involve cutting both flat and curved surfaces or creating edges. The compression measurements are 3/4″. DMI® Dual Cut Foam Coccyx Seat Cushion from www.livehealthsmart.com Place each end of the front section even with one end of a side section. Spray foam adhesive on one edge of the cushion, wait about 10 seconds and then press the fiberfill to that edge. You can use chair upholstery foam almost anywhere you want.