Firmness level 1: Standard hard (SDH) is our standard firmness level and is suitable for regular use by the majority of users from newborns to adults. For the majority of users weighing under 80kg (<176 pounds). Firmness level 2: Special hard (SH) is our middle firmness level and is suitable for users weighing between 80 - 100kg (176 pounds - 220 pounds). This mattress is also suitable for those with minor spinal complications or degeneration. (e.g.back pain). Firmness level 3: Super hard (SSH) is our firmest level and is suitable for users weighing over 100kg (>220 pounds). This mattress is also suitable for those with serious spinal conditions and degeneration.