A capsule for preparing a beverage consists of a capsule body (2), which has a side wall (3) and a bottom (4), and a lid that covers the capsule body for forming a closed chamber, which is filled with a substance. The capsule body made of plastic material is provided with at least one aroma-tight barrier layer. Openings (8) are provided on the bottom (4), through which openings liquid can flow in a beverage preparation machine in addition to the openings that are created by a penetration means (12). A likewise aroma-tight membrane (9) for sealing the closed chamber (6) with respect to the opening (8) is arranged on the inside of the bottom (4). Said membrane is connected to the bottom either along a connection zone (10) following the circumference of the bottom or over the entire area.