An overly firm seat or mattress creates uncomfortable pressure points (above) that cause restless tossing and turning. The right firmness (below) is more relaxing and restful.
Ergocheck Testing uses a specially designed pad with hundreds of tiny sensors that measure the physical pressure between the body and a specific seat or mattress firmness. Although it is predominately used to choose the right mattress firmness the results can be used as a guideline for seat cushions as well. Choose a firmness based on your weight, preference and the test results.
For example, if you weigh between 140 to 180 lbs, you would fall in the medium category. Your firmness options (the last 2 numbers of the foam) would be between 24 and 30 ILD (Indentation Load Deflection). You can choose lower or higher in your range or from the next range based on your preference, foam thickness, and the intended use of the foam.
Keep in mind, Back Foam does not need to be as firm as a Seat Foam because it does not support as much weight. Also a seat needs to be firmer than a mattress because there is more weight concentrated in one spot.
If you go too far from your weight range or too firm, you will get uncomfortable pressure points that will cause you to toss and turn excessively and prevent you from sitting or sleeping comfortably.