The thermal performance of solar heating systems is strongly influenced by the thermal stratification in the heat storage. The higher the degree of thermal stratification is, the higher the thermal performance of the solar heating systems. Thermal stratification in water storages can for instance be achieved by use of inlet stratifiers combined with low flow operation in the solar collector loop. In this paper, investigations of a number of different fabric stratification pipes are presented and compared to a non flexible inlet stratifier. Additional, detailed investigations of the flow structure close to two fabric stratification pipes are presented for one set of operating conditions by means of the optical PIV (Particle Image Velocimetry) method.