A bulk container bag (1) of flexible fabric is provided with shape retaining flexible fabric strips (11) at the corners (7) to prevent distortion of the filled bag. Each corner is provided with a plurality of shape retaining rectangular strips anchored at their opposed ends (12) to the adjacent side walls (4) and extending across the corner. The strips are mounted one atop the other and spaced apart sufficiently to enable fill material to flow freely in and out of the corners to have complete filling and packing so that the bags will retain their shape even when stacked. The shape of the strips ensure uniform tensile forces on the walls from top to bottom of the strip.
