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Glossary · F

Flange

What it means, when you'll hear it, and what it actually changes in practice.

Written & reviewed by Lisa Adair — IBCLC, paediatric sleep consultant & registered NICU nurse · Last reviewed 19 June 2026

A flange is the funnel-shaped part of a breast pump that fits over the nipple and areola to form a seal so the pump can draw out milk.

A flange is a key part of a breast pump. Shaped like a funnel, it fits over the nipple and surrounding breast to create a seal, so that when the pump cycles it can draw milk out through the nipple into the attached container.

Why does size matter?

Flanges come in a range of sizes, matched to the diameter of the nipple. A flange that fits correctly lets the nipple move freely without excessive rubbing, which supports more comfortable and effective expressing. One that is too small or too large can cause discomfort, soreness or reduced milk output.

How do you know it fits?

A reasonable fit generally allows the nipple to move in and out of the flange tunnel freely, with little of the surrounding areola being pulled in and without pinching or pain. Nipple size can change over time, so the size that fits best may also change during a feeding journey.

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