Flexible bulk containers

A flexible bulk container comprising a tubular side wall structure of a square woven polypropylene fabric, with warp threads extending from top to bottom of the side wall structure and weft threads extending around the side wall structure, lifting means at an upper end of the side wall structure, and a base closing the lower end of the side wall structure, the base being in the form of a polygon having an even number of sides and comprising a plurality of thicknesses of said woven fabric, each thickness being 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 which, in each thickness of the base, each flap is of substantially right-angled triangle shape having a first adjacent side lying alone 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, the hypotenuses of the flaps being on the bias with respect to the fabric, and the resulting seam being a bias seam.