What does mattress firmness mean: soft, medium, firm, or extra firm?

Firmness determines how much a mattress gives under your body weight. Revor uses a firmness curve where your weight and height together determine the ideal firmness. Mattresses with a comfort layer of visco, latex, or Waterfresh Foam are naturally softer than those with hybrid foam or HD foam, at the same firmness rating. So it's always the combination of core and comfort layer that determines the final sleep comfort.