Finding the right size is key to maximize comfort and output. Willow offers flanges in three sizes: 21mm, 24mm, and 27mm. If you measure equal or smaller than 21mm, we offer sizing inserts in five sizes (13mm, 15mm, 17mm, 19mm and 21mm) that snap into our 24mm flanges and containers.

We strongly recommend measuring yourself to determine your Willow size, as our sizing may be different than other pumps you’ve used. Use our sizing guide or check out our exhaustive guide on how to measure your flange size, which includes pro tips from Willow’s lactation consultants.

Nipple size can change throughout your breastfeeding journey, often getting smaller over time. If you sized at the hospital and are considering a Willow purchase several months into breastfeeding, it’s time to re-size.

 We recommend re-sizing every three months, or anytime you order a fresh flange or insert. We also suggest re-sizing whenever you experience an unexpected change in volume or comfort, as that may indicate an incorrect flange size.

Willow 360 offers complete leak-free mobility when pumping with our Spill-Proof Milk Bags. With its patent-pending latch technology, you can pump in any position, from bending over to laying down. Willow Go does not offer the same 360° mobility — instead, it offers 45° of leak-proof mobility for moms who will not be moving as much when pumping.

Willow 360 also offers more milk storage options. It’s compatible with our Spill-Proof Milk Bags and reusable containers, while Willow Go is only compatible with reusable containers.

Both pumps are app-connected, but Willow 360 is built with smart sensors that send real-time output information to the app — allowing you to track your milk volume while you pump. When pumping with Willow Go, you can enter your volume manually. Finally, you can manage your session from your Apple Watch when using Willow 360, while Willow Go can only be controlled via the app on your phone.

Willow pumps are unique because everything works inside the pump, inside your bra—no external tubes, cords, or dangling bottles. Plus, you don’t have to sacrifice performance. Willow 360™ and Willow Go™ offer hospital strength suction comparable to most double-electric and hospital-grade pumps - choose from seven levels of adjustable suction with Willow 360, or nine levels with Willow Go. They’re also easy to assemble and clean, and app connected.