Starting piece (100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) to form a container (174) for microwave heating, comprising: a series of joined panels, each panel having of the series of panels joined a first dimension that extends in a first direction and a second dimension that extends in a second direction substantially perpendicular to the first direction, the series of panels attached including a main panel (102, 302, 402, 502, 602, 802, 902, 1002), a first minor panel (106, 206, 306, 406, 506, 606, 806, 906) attached to the main panel, a second minor panel (108, 208, 308, 408, 508, 608, 708, 808, 908) attached to the main panel, and a major panel (104a, 304a, 404a, 504a, 604a, 804a, 904a) attached to the first minor panel, in which the main panel, the first panel minor, the second minor panel, and the major panel are respectively attached to each other along a series of respective fold lines, substance In parallel, (110, 112, 114, 910, 912, 914) extending in the first direction, and an end panel (136, 1036) attached to the main panel along a substantially curved folding line (138) which extends, in general, in the second direction, the end panel having an end edge (140) opposite the curved folding line； and an element (168) interactive with the microwave energy that is arranged above, at least one of the joined panels, characterized in that the second dimension of the end panel increases from the curved folding line to the extreme edge.Pieza inicial (100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) para formar un recipiente (174) para el calentamiento por microondas, que comprende: una serie de paneles unidos, teniendo cada panel de la serie de paneles unidos una primera dimensión que se extiende en una primera dirección y una segunda dimensión que se extiende en una segunda dirección sustancialmente perpendicular a la primera dirección, incluyendo la serie de paneles unidos un panel principal (102, 302, 402, 502, 602, 802, 902, 1002), un prim
