A process can be used for preparing thermally insulating articles containing a thermally insulating polyurethane foam producible in place, a casing surrounding the thermally insulating polyurethane foam, and a foam separator located within the thermally insulating polyurethane foam. The thermally insulating articles producible according to this process are useful. Corresponding cooling systems like fridges, heat storage systems, insulation panels for construction, insulated pipes, mobile transport systems, water boilers, burners, chimneys, instrument panels, roofs of industry hails, engines, or caravans contain the thermally insulating article.