Abstract: The mattress comprises two successive, coupled and superimposed layers (6, 7), each layer being formed from a fluidtight surrounding wall. The first layer (6), adapted to receive the body of the user, contains a plurality of adjacent but separate air bubbles (8) having a substantially identical volume at all points of the layer. The second layer (7) contains air bubbles (10) which are adjacent and separate but have different volumes according to their location in the second layer. The bubbles of the second layer have a volume proportional to the relative density of the various parts of the body of the user stretched out on the mattress. Application in medical uses or swimming pool or seaside amusement.