Holds you on top of the mattress with barely an inch of give.
Measurement
often numbered 7 to 8 of 10 on a seller's own scale
The basics
What to know about firm
Firm sits near the hard end of a lineup: a thin comfort layer, a dense core, and a surface that pushes back almost at once. You sleep on the mattress rather than in it, and the outline of your body barely shows when you get up.
Support comes from the core, not the top. Firmer coils, higher-density foam or a shallow quilted layer produce it. Heavier sleepers reach that core in any bed. That is why one mattress reads medium to a 250-pound sleeper and firm to a 130-pound one. Firmness is a relationship between the bed and your weight, never a property of the bed alone.
Behavior is easy to predict. The midsection stays level, which suits back sleepers and matters most to stomach sleepers, whose hips otherwise drop and arch the lower back. Repositioning is effortless because there is no hollow to climb out of. Edges stay strong enough to sit on while you tie shoes. Airflow also improves because less of your body is enclosed.
Pressure is the price. Side sleeping puts your full shoulder weight onto a surface that will not move. A numb arm or an aching shoulder shows up within an hour or two. The fix works, though. A 2 to 3 inch topper softens a firm bed convincingly. That makes firm the safer error of the two if you must buy without lying on it.
Best for
When it works well
Stomach sleepers, whose hips drop and arch the lower back on anything softer.
Back sleepers who want the midsection held level rather than cradled into a hollow.
Heavier bodies over roughly 230 pounds, which sink into a medium bed until it behaves like a plush one.
Anyone who repositions often, since there is no hollow to climb out of on every turn.
Hot sleepers, because less of the body is surrounded by padding and air moves more freely around it.
