Ceramic microsieves with slit-shaped perforations were compared to sieves with circular-shaped perforations, regarding flow resistance and membrane strength. Destructive tests show that the highest strength is obtained if the perforations are placed in a non-alternating pattern. Especially for slits, alternating patterns should be avoided as they make the structure unnecessarily flexible. The highest stress occurs at the edges of the membrane where it is attached to the support. Flexible structures bend stronger and therefore cause a higher stress at the edge, resulting in an easier rupture of the membrane. Our results show that ceramic microsieves with slits show a four to five-fold decrease in flow resistance for comparable strength related to sieves with circular pores.