Method of forming a thermal insulating device

Method for making a thermal insulating unit or a device containing such a unit, said unit comprising a core of open celled organic foamed insulating material located between outer and inner walls of the unit, comprising the steps of

• a) foaming of insulating material in a cavity between the outer and inner walls of the unit;
• b) evacuating the foamed cavity;
• c) refilling the foamed cavity with an insulating gaseous composition and,
• d) sealing the cavity wherein the open celled organic foamed insulating material comprises open celled rigid polyurethane or urethane-modified polyisocyanurate foam prepared by reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive composition in the presence of an isocyanate-reactive cyclic compound of formula (I) ##STR3## wherein in formula (I) Y is O or NR.sup.1 where each R.sup.1 independently is a lower alkyl radical of C.sub.1 -C.sub.6 or a lower alkyl radical substituted with an isocyanate-reactive group;
• each R independently is hydrogen, a lower alkyl radical of C.sub.1 -C.sub.6 or (CH.sub.2).sub.m --X wherein X is an isocyanate-reactive group which is OH or NH.sub.2 and m is 0, 1 or 2, and n is 1 or 2;
• with the proviso that at least one of R.sup.1 or R is or comprises an isocyanate-reactive group, and
• wherein the method is performed in the presence of a cell opening agent selected from the group consisting of fatty acids, fatty acid amines, fatty acid amides and fatty acid esters.