If you need to replace the foam in your coach cushions, here is a very good article on foam: http://www.carrscorner.com/foam.php It explains the three performance tests that make up foam: High Resilient (HR), Density, and Indentation Load Deflection (ILD).
One recommendation is to consider memory foam. This is not the memory foam as used in mattress toppers (which is fairly low density), but rather is higher density memory foam. It goes by several trade names, TempurFoam, NASA foam, Confor, etc. and is available in several densities. Green is extra firm, then blue, pink, yellow (soft). Memory foam "flows" and conforms so as not to create hot spots. You can sit in comfort for hours - - in fact, it's used for wheelchair pads and for hospital patients to help prevent bed sores.
Most any reputable upholstery shop can provide the type of foam desired for your cushions.
Contributors: Linda Hylton, bumper, Beth
Revised 21 Jul 2011