Hermetically closed package to be heated in a microwave oven

Hermetically closed package enclosing a product (2), especially a food product, to be heated in a microwave oven while being enclosed in said package, said package comprising a wall (3) formed of a packaging material including a first polymer film (7) and a second polymer film (10) being co-extensive with the packaging material, the first polymer film (7) having a first surface (8) and a second surface (9), the second polymer film (10) having a first surface (11) and a second surface (12), the first surface (11) of the second polymer film (10) being laminated to the second surface (9) of the first polymer film (7) by means of an adhesive layer (16), said package further comprising a layer of a material generating heat when subjected to microwave radiation, i.e. a heat-generating layer (5) having susceptor effect,

• characterised in that
• a limited region of the first surface or the second surface is provided with the heat-generating layer (5), said heat-generating layer (5) being deposited or printed on first or second surface (8, 9) of the first polymer film (7) or to the first or second surface (11, 12) of the second polymer film (10) and having an extent substantially smaller than the extent of the wall (3) and having an electrical conductivity corresponding to a surface resistance of 4 to 9000 ohms per square measured according to DIN IEC 93, and that the packaging material is provided with a non-through-going or through-going perforation in the first polymer film (7) in the region of the heat-generating layer (5) as seen transversely of the packaging material, and wherein the susceptor effect of the heat-generating layer (5) is selected such that when subjected to a prescribed amount of microwave radiation, the first polymer film (7) and/or the second polymer film (10) are capable of melting, decomposing, softening or weakening to such a degree that the packaging material disintegrates to form a through-going opening there through in line with the perforation in the first polymer film (7).