Key Facts: Mattress Firmness
This page is Mattress Firmness Picks' maintained fact reference — the firmness and construction facts our guides are built on, restated in plain prose. We report support and pressure-distribution facts, never health-outcome claims.
What ILD actually measures
ILD (Indentation Load Deflection) is a defined foam-industry test: the force, in pounds, needed to compress a standard 15-inch by 15-inch by 4-inch foam sample by 25% of its thickness (one inch), using a 50-square-inch circular indenter. It's specified for polyurethane foam under ASTM D3574; latex is commonly tested under a related but distinct protocol, so latex and polyurethane ILD figures aren't always directly comparable. Higher ILD means firmer foam. Full explainer: What Is ILD?
Self-reported firmness isn't standardized
A brand's 1-10 number or Soft/Medium/Firm label is entirely self-assigned — no accredited body audits it or standardizes it across brands. A "6" from one brand is not measured against the same scale as a "6" from another. Treat a brand's number as informative only within that brand's own lineup. More in What Does Firmness "7" Actually Mean? and Why Firmness Scales Aren't Standardized.
Most brands don't disclose ILD
Non-disclosure of ILD is the norm, not the exception — most consumer mattress brands market with only the subjective label. A minority of brands (Brooklyn Bedding, in this dataset) publish per-layer ILD figures. See the full breakdown in the Firmness Translation Index.
Body weight changes perceived firmness
A heavier body compresses further into any given comfort layer before reaching equilibrium, so the same mattress feels softer to a heavier sleeper than to a lighter one. Rough informal bands: under ~130 lb (lighter), ~130-230 lb (average), over ~230 lb (heavier) — though brands don't standardize these. Details in Does Body Weight Change Mattress Firmness?
Construction changes how a given firmness feels
Identical ILD numbers feel different across constructions: memory foam's slow viscoelastic response deepens the sink-in feeling; latex responds quickly and feels more buoyant; a hybrid's coil support core adds bounce. Some comfort layers (proprietary polymer grids, viscoelastic materials) aren't rated on the standard foam ILD scale at all. See Memory Foam vs Latex vs Hybrid Firmness.
Firmness by sleep position
General equipment-fit guidelines, not medical advice: side sleepers generally do best in the soft-to-medium range for shoulder/hip pressure relief; back sleepers generally do best in the medium to medium-firm range for spinal alignment; stomach sleepers generally do best in the medium-firm to firm range so the midsection doesn't sink and pull the lower back out of line. Details in Best Firmness for Side Sleepers, Best Firmness for Back Sleepers, and Best Firmness for Stomach Sleepers.
No health or medical claims
We describe support and pressure distribution in neutral equipment terms only. A mattress does not treat, prevent, or relieve back pain or any other condition, and we never claim otherwise. For a specific pain or medical concern, consult a physician or licensed physical therapist.
How these facts are maintained
These facts are drawn from manufacturer spec sheets and public product pages, cross-checked against third-party mattress-review aggregators where a brand's own page doesn't state a figure directly, and updated on the date shown above when specs or the market change. We do not publish prices or star ratings, every pick names an honest drawback, and we report firmness/construction facts — never health-outcome claims. Our full methodology is at How We Evaluate Mattresses.