Container preform made of plastic

A container preform (1) made of plastics material, comprising:

• a body (3) exhibiting symmetry of revolution about a central axis (X);
• and
• a bottom (4) closing the body (3) from one of its ends, the bottom (4) having an annular bead (8) forming a standing plane of the preform (1), the bottom (4) having an external skin (Pe) oriented toward the outside of the preform (1) and an internal skin (Pi) oriented toward the inside of the preform (1), the preform having a joint plane (12) at an intersection between the bottom (4) and the body (3), the joint plane (12) having a thickness (EP), wherein:
• at least one of the internal skin (Pi) and the external skin (Pe) has, radially from the central axis (X) as far as the annular bead (8), a profile having a break in curvature, the profile comprising, from the central axis (X) up to the annular bead (8), a first portion (9) having a first radius of curvature, a second portion (10) extending the first portion (9) and having a second radius of curvature, a third portion (11) extending the second portion (10) and having a third radius of curvature;
• the break in curvature being formed by the second radius of curvature presented by the second portion (10), and
• wherein the first portion (9) of the profile has a diameter (d) less than or equal to 40% of a diameter (D) of the preform (1) at the joint plane (12).