Abstract: A flexible bulk container comprises a tubular side wall structure (1 to 4) of woven fabric, lifting means (13) at an upper end of the side wall structure, and a base (14) closing the lower end of the side wall structure. The base is in the form of a polygon having an even number of sides and comprising a plurality of thicknesses of said woven fabric. Each thickness is formed by two joined flaps of woven fabric forming integral extensions of the side wall structure and each extending from one side of the polygon towards the opposed side thereof. In each thickness of the base, each flap is of substantially right-angled triangle shape having a first adjacent side lying along one side of the polygon and a second adjacent side extending at right angles from said one side to the opposed side of the polygon, and the two flaps are secured together substantially along the hypotenuses thereof.