Abstract: An increased volume synthetic fiber consists of a porous central core and a large number of short porous lateral threads integral with the core and distributed along the whole length of the fiber so as to form a voluminous branching structure. The process used to produce the fiber consists of the mixing of a synthetic polymer with an expanding agent which expands when heated, then spinning by melting the mixture which results in the expansion and fringing of the threads produced, caused by the expansion agent, followed by the drawing and fixing of the threads thus produced while they are still hot.