Foam for Upholstery

    You use a much softer foam on the backrest than on a seat because, when you sit on foam you are putting much more weight on the seat foam. By contrast, when you lean against the backrest, you put very little weight against it. (Remember, most of you weight is going to the seat foam.)
     Most seat foam has a firmness rating of aprox. 26 lbs to 30 lbs (soft), 30 lbs to 40 lbs (medium), 40 lbs to 48 lbs (Firm) and 49 lbs to 55 lbs (Extra Firm)
     Conversely, firmness ratings for backrests run about 15 lbs to 20, very soft 20 lbs to 24 (medium-soft)
soft foarm for backs
     So, when you choose a back foam

Foam is Rated by weight and density


Foam Ratings & Usages
Usage Rating Weight   Density   Foam ID 
Seat Cushions Soft 1.5 to 2.5 lb   22 to 30    
  Medium 1.5 to 2.5 lb   30 to 40    
  Firm 1.5 to 2.7 lb   40 to 50    
  Extra Firm 1.5 to 2.9 lb   50 to 55    
Back Cushions Very Soft      10 to 18    
  Medium Soft      18 to 23    
  Firm      23 to 28