Preform for a container made of plastic material, which comprises - a body symmetric in revolution about a central axis, - an open neck that extends in the extension of the body from an upper end thereof, and - a bottom which closes the body from a lower end thereof, the bottom being symmetric in revolution about the central axis and having a central concavity and a projecting bead around this concavity, the bottom having a variable thickness E, measured from an external face, this preform being characterized in that, in any plane of section passing through the central axis, the thickness E of the bottom satisfies the geometric rules (R4.1), (R4.2) and (R4.3) below, where: S is the curved abscissa measured on the external face, from the central axis which serves as the origin; L is the total, curved half-length of the bottom, measured on the external face from the central axis to the lower end of the body; S 1 is a value of the curved abscissa S such that 0.2 · L ≤ S 1 ≤ 0.3 · L; S 2 is a value of the curved abscissa S such that 0.4 · L ≤ S 2 ≤ 0.6 · L; E 0 is the thickness of the preform at the lower end of the body; [0; S 1] is a central section of the bottom, defined by a curved abscissa contained between the origin and S 1; [ S1; S2] is an intermediate section of the bottom, defined by a curved abscissa contained between S 1 and S 2; [S 2;L] is a peripheral section of the bottom, defined by a curved abscissa contained between S 2 and L; (R4.1) in the central section [0; S 1] of the bottom, the thickness E of the preform is such that: 0.65 ⋅ E 0 ≤ E ≤ 0.95 ⋅ E 0; (R4.2) in the intermediate section [S 1; S 2] of the bottom, the thickness E of the preform is strictly less than its value at any point in the central section [0; S 1]; (R4.3) in the peripheral section [ S 2; L] of the bottom, the thickness E of the preform is increasing. - a body symmetric in revolution about a central axis, - an open neck that extends in the extension of the body from an upper end thereof, and - a bottom which closes the body from a lower end thereof, the bottom being symmetric in revolution about the central axis and having a central concavity and a projecting bead around this concavity, the bottom having a variable thickness E, measured from an external face, this preform being characterized in that, in any plane of section passing through the central axis, the thickness E of the bottom satisfies the geometric rules (R4.1), (R4.2) and (R4.3) below, where: S is the curved abscissa measured on the external face, from the central axis which serves as the origin; L is the total, curved half-length of the bottom, measured on the external face from the central axis to the lower end of the body; S 1 is a value of the curved abscissa S such that 0.2 · L ≤ S 1 ≤ 0.3 · L; S 2 is a value of the curved abscissa S such that 0.4 · L ≤ S 2 ≤ 0.6 · L; E 0 is the thickness of the preform at the lower end of the body; [0; S 1] is a central section of the bottom, defined by a curved abscissa contained between the origin and S 1; [ S1; S2] is an intermediate section of the bottom, defined by a curved abscissa contained between S 1 and S 2; [S 2;L] is a peripheral section of the bottom, defined by a curved abscissa contained between S 2 and L; (R4.1) in the central section [0; S 1] of the bottom, the thickness E of the preform is such that: 0.65 ⋅ E 0 ≤ E ≤ 0.95 ⋅ E 0; (R4.2) in the intermediate section [S 1; S 2] of the bottom, the thickness E of the preform is strictly less than its value at any point in the central section [0; S 1]; (R4.3) in the peripheral section [ S 2; L] of the bottom, the thickness E of the preform is increasing. S is the curved abscissa measured on the external face, from the central axis which serves as the origin; L is the total, curved half-length of the bottom, measured on the external face from the central axis to the lower end of the body; S 1 is a value of the curved abscissa S such that 0.2 · L ≤ S 1 ≤ 0.3 · L; S 2 is a value of the curved abscissa S such that 0.4 · L ≤ S 2 ≤ 0.6 · L; E 0 is the thickness of the preform at the lower end of the body; [0; S 1] is a central section of the bottom, defined by a curved abscissa contained between the origin and S 1; [ S1; S2] is an intermediate section of the bottom, defined by a curved abscissa contained between S 1 and S 2; [S 2;L] is a peripheral section of the bottom, defined by a curved abscissa contained between S 2 and L; (R4.1) in the central section [0; S 1] of the bottom, the thickness E of the preform is such that: 0.65 ⋅ E 0 ≤ E ≤ 0.95 ⋅ E 0; (R4.2) in the intermediate section [S 1; S 2] of the bottom, the thickness E of the preform is strictly less than its value at any point in the central section [0; S 1]; (R4.3) in the peripheral section [ S 2; L] of the bottom, the thickness E of the preform is increasing.