The invention relates to a flexible container for fluids, comprising an inner bag (1) of a thin material and an outer sack (2) of a durable fabric. The outer sack (2) is cylindrical and its mantle surface is provided with channels (4) for receiving support pillars (5) fastened to a wooden pallet (6). At deceleration during the transport of a full container, the upper ends of the forward support pillars exert great spot loads on the outer sack (2). Such loads can be avoided to a great extent if an outer and an inner side wall (8, 9) of the channels (4) are equally broad in the peripheral direction of the outer sack.