Abstract: A method of producing a flexible heat-exchange device including a body having a flexible mats and an internal passageway for heat-carrying fluid, an inlet and an outlet, including placing first and second plastic elastic mats in a mould die having supporting surfaces and recesses around the supporting surfaces, separating the first and second plastic elastic mats by a resilient counterdie, bringing the mould dies together with the first and second plastic elastic mats separated by the resilient counterdie into contact wherein the first and second plastic elastic mats are stretched down around abutment surfaces by deformation of the resilient counterdie and around the support surfaces and down into the recesses so as to obtain local plastic deformations as the mould dies are brought together, placing the second plastic elastic mat over the first plastic elastic mat, and mutually joining the first and second plastic elastic mats to form the body.