In recent years a trend towards more comfortable beds and mattresses has been developed. Water-filled warming mattresses have proofed to increase the comfort of beds. With the climate change, the number of nights with high temperatures during the summer is increasing. SBI has proposed to develop a water-circulated heating / cooling mattress to allow for comfort during both cold winter and hot summer nights. SBI has extended know-how about mattress heating systems. Cooling aspects are new to SBI. The introduction of such a mattress requires investigation of contact pressure / pressure points, comfort ratings in relation to cooled surface temperature, cooling requirements and heat exchanger surface design next to working principle requirements.