An inexpensive inner bag loaded into a cylindrical container such as a drum. The inner bag has excellent airtightness and facilitates transferring the inner bag to a separate container. The inner bag comprises two hexagonal first sheets (7) and two pentagonal second sheets (9). Each first sheet (7) has a pair of opposite sides (3a, 3b) extending extending longitudinally and a trapezoidal portion (5a) formed around one longitudinal end (11c) of the sheet (7). Each second sheet (9) has a pair of opposite sides extending longitudinally and a triangular portion (5b) formed around one longitudinal end (11d) of the sheet (9). The first (7) and second (9) sheets are placed in an opposite relation to each other. The peripheries of the first (7) and second (9) sheets, excluding the other ends (13a, 13b), are bonded together by heatsealing.
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