The OptiFit Set and Promise provides the solution to your endless flange sizing madness, giving you the "Optimal" fit every time! What's so unique about this set is the angled shape of the flange, designed to fit your natural shape while allowing you to lean back and relax while pumping. We've also taken into account the natural fluctuations that can occur throughout a breastfeeding journey. If one or both breasts ever become uncomfortable with a flange size that used to work well, even for a day — you'll already have what you need to ensure better flow and reduced irritation. All Pumpin' Pal flanges are made in the USA from USA sourced BPA free silicone and polypropylene. Note: X-Small and Small flanges are silicone, the Medium flange is rigid polypropylene.