A novel composite of glass fiber paper and reinforcing material that is useful for high speed manufacturing of devices comprising it is disclosed. The composite is formed by pressing into a glass fiber paper, having multimodal (at least bi-modal) composition, a hydrophilic reinforcing material. The composite has anisotropic separation properties that are particularly useful for preparing a fluid fraction from whole blood. The preferred glass fiber paper comprises glass fibers such that there are a plurality of short fibers (6) having large diameters and long fibers (2) with smaller diameters. The preferred glass fiber paper also exhibits partial ordering. There are many more of the long fibers (2) with smaller diameters than of the short fibers (6) having large diameters. Also disclosed are several blood separator device designs for efficiently separating the fluid fraction of blood from whole blood using the composite.