Willow Breast Pump Sizing Kit Review – Flange Inserts That Actually Help
Willow - Breast Pump Sizing Kit - Flange Sizing Kit - Use w/Willow Go, Wave, or Most 24mm Flanges - Includes 13mm, 15mm, 17mm, 19mm, and 21mm Inserts- Breastfeeding Essentials for Postpartum
Willow
- Experiment with 5 sets sizing inserts; Includes 2 each of 13mm, 15mm, 17mm, 19mm, and 21mm Inserts
- Nipple Sizing Tool to easily find your fit; Connect with a Sizing Specialist for personalized guidance
- Use with Willow Go, Willow Wave, Willow 360 or any pump; they’re compatible with almost all 24mm flanges
- Pump Sizing 101 Guide with everything you need to know about maximizing comfort
Quick Verdict
Pros
- Covers 5 flange sizes (13mm to 21mm) so you can experiment without buying separate kits
- Includes a printable nipple sizing tool to find your baseline fit
- Compatible with Willow Go, Willow Wave, Willow 360 and most standard 24mm flanges
- Comes with a Pump Sizing 101 Guide explaining why fit matters for comfort and output
- Two of each insert size included — ideal for testing both breasts if they differ
- Access to Willow's Sizing Specialist adds a helpful human touch
Cons
- Only works with 24mm base flanges — not helpful if you need much smaller or larger starting sizes
- The sizing tool requires some visual judgment, which can feel imprecise for some users
- Kit does not include a storage case, so smaller inserts are easy to misplace
- At around $40, it is a notable add-on cost for parents already spending heavily on feeding gear
Quick Verdict
The Willow breast pump sizing kit is a focused, practical tool for any pumping parent who has ever stuffed themselves into the wrong flange and wondered why pumping felt like a punishment. It does one job: help you find the size that fits your body. After spending time with the inserts, the sizing tool, and the included guide, I can say it does that job well — as long as your pump uses a 24mm base flange. Check current price and availability on Amazon.
What Is the Willow Breast Pump Sizing Kit?
The Willow sizing kit is a collection of 10 silicone inserts — two of each in five sizes (13mm, 15mm, 17mm, 19mm, and 21mm) — designed to reduce the inner diameter of a standard 24mm breast pump flange. Think of each insert as a sleeve that snaps inside your existing flange, narrowing the tunnel your nipple draws into without requiring you to buy an entirely new set of flanges in every size.
Willow also bundles a nipple sizing tool: a printed guide with circular cutouts you hold up to your nipple to see which size corresponds to your measurements. Alongside this is a Pump Sizing 101 guide that explains why flange fit affects comfort, milk flow, and overall supply. The kit is primarily marketed for Willow Go and Willow Wave users, but the inserts are built to fit any 24mm flange — which covers a wide range of pumps beyond the Willow ecosystem.
Key Features
- 10 inserts total: 2 each of 13mm, 15mm, 17mm, 19mm, and 21mm
- Nipple sizing tool included to find your starting point
- Pump Sizing 101 Guide explains fit, comfort, and output connections
- Compatible with Willow Go, Willow Wave, Willow 360, and most 24mm pump flanges
- Medical-grade silicone — boilable, steam-sterilizable, dishwasher safe
- Access to Willow Sizing Specialist for personalized support
Hands-On Review
I will be honest — the sizing kit sat on my desk for two days before I actually opened it. Flange sizing felt like one of those things I should already know how to do, so there was a quiet embarrassment in admitting I had been pumping with the wrong size for weeks. That hesitation is worth naming because Willow clearly designed this kit for exactly that moment: when someone is suffering in silence and does not know there is a better way.
The nipple sizing tool is straightforward in concept but slightly awkward in practice. You align the circular cutout over your nipple and read the size indicated — the trick is doing it without the tool slipping, which can happen if you are trying to hold a mirror and a phone torch at the same time. The guide does warn you about this, suggesting you photograph your measurement for reference, which I ended up doing and found genuinely useful.
Once I had my baseline size, I started testing. I had been using 21mm flanges with my Willow Go and was curious whether going down would make a difference. Within the first three pumping sessions using the 17mm inserts, I noticed two things: the pulling sensation was noticeably less sharp, and my output did not drop — something I quietly worried about before I started. By the end of the first week, I had essentially retired the larger inserts. Will I keep using them? I suspect I will, though the 15mm inserts may be worth a try if the 17mm starts feeling too loose.
The silicone inserts snap into the flange cleanly and stay in place during a session. Cleaning them is simple — I ran them through the dishwasher twice and boiled them once without any warping or smell retention. They feel durable enough for daily use, though I am only three weeks in at this point, so long-term elasticity over months is something I cannot fully assess yet.
What surprised me was how much the Pump Sizing 101 guide added to the package. It is not marketing fluff — it explains the mechanics of why a too-large flange causes friction, how that relates to inflammation and output, and what to look for if your size changes over time. For a new parent who has never been taught this, it is genuinely informative.
Who Should Buy It?
- New pumping parents who have never been properly sized and want to start with a baseline before buying flanges separately
- Hands-free pump users (especially Willow Go or Wave owners) who want to fine-tune their fit without replacing whole flange sets
- Anyone experiencing discomfort, friction, or lower output during pumping sessions and suspects flange size may be the cause
- Parents whose bodies changed through pregnancy, postpartum recovery, or milk supply fluctuations — size can shift, and this kit lets you adapt without a new purchase each time
Skip this if you already know your exact flange size from a lactation consultant or pump fitting, and you have purchased the correct flanges already. It is also not useful if your pump uses non-24mm flanges, as the inserts will not fit.
Alternatives Worth Considering
- Lactation Lab Custom Flange Kit — a solid alternative if you want professionally measured custom flanges rather than experimenting with inserts; better for parents who want a one-and-done solution rather than a sizing journey
- Maymom Breastshield Sizing Set — offers a broader range of sizes including smaller options not covered here; a practical choice if you suspect you need below 13mm
- Medela PersonalFit Flex Connectors — if you use a Medela pump, Medela's own sizing inserts and connector system may integrate more cleanly with your existing setup than third-party options
FAQ
The kit includes 2 inserts each of 13mm, 15mm, 17mm, 19mm, and 21mm — so 10 inserts total, covering a broad range of nipple sizes for most pumping parents.
Final Verdict
The Willow breast pump sizing kit solves a real problem that the breastfeeding industry has largely ignored: most parents are never properly taught that flange size is personal, varies between breasts, and changes over time. By bundling inserts, a sizing tool, and an educational guide into one kit, Willow has made the process of finding your fit accessible and relatively low-stakes. The $40 price tag is not trivial, but compare it to buying three or four individual flange sets guessing blind — the math leans in favour of the kit. If you use a 24mm-based pump and have any doubt about your current flange fit, this is a worthwhile and practical purchase.