The present invention relates to a rheology additive, according to which A) said additive consists of: a) at least one symmetrical fatty diamide of formula (I): (AGH)—CONH—(PMDA)-NHCO-(AGH) (I) with: (AGH): hydroxylated fatty acid residue R1CO2H, without —CO2H group, with R1 of C18 to C20 comprising a hydroxyl group, —NHCO— or —CONH—: amide group, —(PMDA): residue without amine groups of 1,5-pentamethylenediamine; or alternatively according to which: B) said additive comprises: a) at least one symmetrical fatty diamide as defined above according to formula (I) and, in addition, b) at least one other symmetrical fatty diamide of formula (II): (AGH)—CONH—(R)—NHCO-(AGH) (II) with (AGH), —NHCO— and —CONH— having the same definition as that above in said formula (I), and (R) being the residue without amine groups of a diamine, other than (PMDA), chosen from a cycloaliphatic, aliphatic or aromatic diamine.