Preform provided with a concave body portion

Container preform (1) made of plastic material, which comprises:

• a symmetrical body (3) of revolution around a central axis (X);
• an open neck (5) that extends in continuation of the body (3) from which it is separated by a radial protruding flange (6);
• a bottom (7) that closes the body (3) opposite the neck (5);
• wherein the body (3) has a portion (11) that is concave in axial section and wherein:
• B≤0.9·A
• 0.5 ·C≤C′≤0.95·C
• where:
• A is the overall diameter of the body (3), measured under the flange (6);
• B is the outer diameter of the bottom (7), measured at its junction with the body (3);
• C is the cumulative height of the body (3) and the bottom (7), measured from the flange (6);
• C′ is the height, measured axially, of the concave portion (11) of the body (3),
• and wherein the concave portion (11) has, in axial section, on an outside surface (10), an outside radius of curvature RE such that:
• 1.5·C≤RE≤10·C.