A method of manufacturing footwear by a mold (1 and 2) and a counter-mold is in the form of a last (3), between which the pieces (4 and 5) that will form the upper are arranged. These pieces define channels (9) between one another which, together with cavities (10 and 11) demarcated between mold and counter-mold, determine a network of channels and cavities into which a thermoplastic material in molten state is injected.