Pneumatic seat cushion system

A pneumatic seat cushion system comprising

• (a) a deformable cushion having a seating surface for resting the buttocks and legs of a seated person,
• (b) a self inflating cushion bladder positioned beneath the seating surface, the self inflating cushion bladder comprising an airtight envelope containing compressible material which is in air communication with a displacement bladder such that when in use the airtight envelope and the displacement bladder form a closed system from which no air can enter or escape;
• the arrangement being such that when there is no weight applied to the seating surface, the self inflating cushion bladder is configured to self inflate and the displacement bladder is configured to deflate such that the self inflating cushion bladder is fully inflated while the displacement bladder is deflated and that when weight is applied to the seating surface, as when a person is seated on the seating surface, the weight on the seating surface compresses the compressible material so as to partially deflate the cushion bladder and displace sufficient air from it into the displacement bladder via one or more air passageways formed between the cushion bladder and displacement bladder, until the displacement bladder is fully inflated.