A single-lobe filter bag for infusion products comprises a length (2) of filter material forming a chamber (3) containing a charge (4) of the infusion product. The length (2) comprises: a first closed top end (5) formed by a first join (S1) between two first end edges of the length (2); a second closed bottom end (7) and two sides (8, 9) connecting the two ends (5, 7) of the length (2); the two sides (8, 9) connecting the first and second edges (5, 7) are at least partly folded onto each other to form a fold towards the inside of the chamber (3) and the second bottom end (7) of the filter bag (1) is closed by a second join (S2) designed to form a rigid flat bottom surface (11) of the filter bag (1) such as to define a stable base, with a substantially triangular cross section, for supporting the filter bag (1).