It is well known that using the correct breastshield size is for your pumping comfort and optimal milk supply. We include two 25 mm breast shields that will be more comfort and suitable for the majority of breast feeding mothers. Compared to medela valve our design of valve allows your precious milk to flow easier into the bottle. The pump in style substitute tubing set will fit medela pump in style and pump in style advanced breastpump. Maymom breastshields can be connected with medela storage bottles and other standard-szied bottles like gerber playtex and ameda. They are compatible with medela valve and medela membrane. Maymom is not affiliated with medela.