A breast cup for an undergarment, such as a brassiere, includes a cup core that has a first surface and a second surface opposite the first surface. Each of the first and second surfaces is formed with a plurality of grooves. Each groove has an elongated opening, an elongated bottom, and a sidewall on each of two longitudinal sides of the groove. The breast cup also includes a first fabric layer overlying the first surface of the cup core, and a second fabric layer overlying the second surface of the cup core. A top part of the sidewalls of one or more of the plurality of the first grooves is attached to the first fabric layer while at least a portion of the bottom of the one or more of the plurality of the first grooves is not attached to the first fabric layer.