Abstract: This invention relates to a container having at least one inlet and/or outlet and containing at least two different solids arranged in layers as well as the use of said container for preparing a dialysate. In particular, a flexible bag is described, having three layers of different solids, where the middle layer consists of a solid which is compatible with the two adjacent layers and thus forms a separating layer between the two other layers. The layers are secured in place during shipping by vacuum packing.