Disclosed is a preform for a plastics container, which includes: a rotationally symmetrical body about a central axis; an open neck which extends in continuation of the body from an upper end of the latter; a bottom which closes the body starting from a lower end of the latter, the bottom being rotationally symmetrical about the central axis and having a central concavity and a protruding bulge around this concavity, the bottom having a thickness E, measured from an external face, that is variable in accordance with three different criteria respectively applied to three sections of the bottom, namely a central section [0; S1], an intermediate section [S1; S2] and a peripheral section [S2; L].