A capsule containing a substance for the preparation of a potable beverage by extracting and/or dissolving the substance by means of supplying a fluid under pressure into the capsule (2; 102; 202), the capsule comprising: an aluminum capsule body having a central capsule body axis, the aluminum capsule body comprising a bottom, a side wall (16; 116), an outwardly extending flange (20; 120; 220) and a sealing structure (28; 128; 228) at the flange; and a cover sheet (14; 114) attached to the flange (20; 120; 220) and hermetically closing off the capsule (2; 102; 202); wherein the sealing structure (28; 128; 228) is deformable for providing a fluid sealing contact with an annular end surface of an enclosing member of a beverage preparation device if the capsule (2; 102; 202) is positioned in the enclosing member and the enclosing member is closed by means of a closing member of the beverage preparation device, such as an extraction plate of the beverage preparation device, at least portions of the flange (20; 120; 220) and the sealing structure (28; 128; 228) being clamped between the annular end surface and the closing member said end surface of the annular element optionally being provided with a plurality of radially extending open grooves; wherein the sealing structure (28; 128; 228) includes a deformable sealing ring portion of the flange (20; 120; 220), the sealing ring portion comprising a layer of aluminum sheet material (44; 144; 244) contiguous with the side wall and at least one resilient layer (45; 145; 245); characterized in that said at least one resilient layer (45; 145; 245) is located between the layer of aluminum material and the cover sheet (14; 114) and has a thickness larger than the thickness of the layer of aluminum sheet material (44; 144; 244). an aluminum capsule body having a central capsule body axis, the aluminum capsule body comprising a bottom, a side wall (16; 116), an outwardly extending flange (20; 120; 220) and a sealing structure (28; 128; 228) at the flange; and a cover sheet (14; 114) attached to the flange (20; 120; 220) and hermetically closing off the capsule (2; 102; 202); wherein the sealing structure (28; 128; 228) is deformable for providing a fluid sealing contact with an annular end surface of an enclosing member of a beverage preparation device if the capsule (2; 102; 202) is positioned in the enclosing member and the enclosing member is closed by means of a closing member of the beverage preparation device, such as an extraction plate of the beverage preparation device, at least portions of the flange (20; 120; 220) and the sealing structure (28; 128; 228) being clamped between the annular end surface and the closing member said end surface of the annular element optionally being provided with a plurality of radially extending open grooves; wherein the sealing structure (28; 128; 228) includes a deformable sealing ring portion of the flange (20; 120; 220), the sealing ring portion comprising a layer of aluminum sheet material (44; 144; 244) contiguous with the side wall and at least one resilient layer (45; 145; 245); characterized in that said at least one resilient layer (45; 145; 245) is located between the layer of aluminum material and the cover sheet (14; 114) and has a thickness larger than the thickness of the layer of aluminum sheet material (44; 144; 244).