Visco-elastic foam is an interactive PU-foam, which, under the influence of heat, softens and changes shape. Where the foam is in contact with (body) heat (and pressure) the cells become more flexible. They shape according the contours of the body that produces heat and pressure. The counter-pressure of the visco-elastic foam is low in comparison to other types of polyurethane foam. If the pressure and heat have been removed, the foam will return to its original shape; which explains why this type of foam is also referred to as a memory foam. The response capacity of the foam is dependent on the foam formulation, and the room temperature. Sensus is a type of visco-elastic foam with an open cell structure. Also, the composition of Sensus ensures that the foam does not turn very firm at lower temperatures. Sensus is available in different degrees of density and hardness, and in a flame retardant version.