Density and firmness are commonly confused.

Foam density and firmness are two completely different measurements.

Most mattress manufacturers using memory foams increase the foam’s firmness as they increase density.

• As a result the ILD (Indentation Load Deflection) “firmness” rating becomes irrelevant to their customers.

Memory foam density is measured as mass per unit volume (lb./cubic ft.)

• The higher the density, the more foam material is used within a given volume.
• Higher density foams will be heavier than lower density foams.
• Higher density foams are more durable than lower density foams.
• Higher density foams are more expensive than a lower density of the same type of foam.

Memory foams have higher densities than non-memory polyurethane foams.

• “High density” polyurethane foams (commonly used in seat cushions) range from 1.8 – 2.8 for most residential furniture.
  • Heavier duty commercial and institutional furniture may use polyurethane foams that are 3.0 or higher.
• “High density” memory foams (more commonly found in mattresses) begin at 5.
• Memory foams used in mattresses can range anywhere from densities of less than 1.5 to 8 lb.
  • Most memory foam mattresses have a density ranging from 3 -5.
  • There is a significant increase in price as foam density increases.

  A foam’s firmness is measured by its indentation load deflection (ILD) rating.

  • ILD is not a straightforward measurement of “soft” vs. “firm.”
    • When comparing two foams with identical densities the one with the higher ILD will feel firmer when compressed.
    • When comparing two foams with identical ILD “firmness” ratings but different densities, the foam with the higher density will feel firmer.
  • ILD ratings for memory foams in mattresses generally range between super soft (ILD 10) to extra firm (ILD 18.)
    • ILDs of 50 can be found in memory foam used in automobile seats.
  • ILD ratings for polyurethane foams in cushions typically range from 25 – 40.

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