one element and one processing stage connected with the application of the latter with the consequent possibility of obtaining more rapid and economical production and 4 the ability of the skier to replace the leg of the boot with another of equal or different height contour or color without having to return the boot to the factory the boot upper 1 according to the invention is manufactured using a traditional mold comprising two withdrawable lateral elements 12 fig3 to 5 an inner former 13 and a piston means not shown this assembly provides an interspace 14 which constitutes the negative of the molded article to be obtained the lateral mold elements 12 are shaped in such a way that the upper is obtained with its two front sides 15 joined together a blade 16 partially projecting from the inner former 13 produces a groove 17 between the two sides 15 to facilitate their separation to obtain the boot according to the invention the constituent material polyurethane or the like of the upper 1 is injected into the mold and shortly before it has completely solidified the two lateral mold elements 12 are pulled apart so that the flanges 7 of trunnions 5 can withdraw from the corresponding seat 18 of elements 12 overcoming the undercut resistance induced by the flanges 7 such flexure of the partly solidified elements 7 during mold separation is graphically shown in fig4 finally the two front sides 15 of the upper are cut longitudinally to separate them by exploiting the weakness of the upper at the groove 17 in a modified embodiment of the invention diagrammatically shown in fig6 the positions of the mushroom like elements 5 39 and coacting holes 9 39 are.