A system for assisting a user in the determination of a thickness of a layer of insulation, the determination being in compliance with design requirements for an object to be insulated, comprises: data input means, for receiving from the user, input data representing boundary conditions relating to the insulated object, the input data receiving means comprising predetermined insulation data storage means from which the user can select predetermined insulation data relating to the insulated object, means for calculating, on the basis of the input data, insulation thickness data to be output to the user; and display means for displaying the calculated insulation thickness data alongside a graphical representation of the predetermined insulation data, wherein the data input means comprises means for varying, by the user, the input data by selecting differing predefined insulation data items displayed in the graphical representation, to thereby vary the insulation thickness data to be output to the user.