If you're only getting a little bit of milk or not fully emptying, then one or more of the following factors could be at issue:

  • Improper cup assembly
  • Incorrect flange fit
  • Poor bra fit
  • Incompatible pump
  • Flange design
  • Device health
  • Conditioned response

Cup Assembly

Review correct cup assembly here. Parts must all be pushed together firmly. For example, Step 3 below (for pink or blue SlimFit Cups) is critical to proper suction. (Click image to enlarge.)

Flange Fit

Finding the right breast flange size is a lot like finding the right bra size — they vary between brands, some brands don't feel as good as others, you may be perfectly asymmetrical, or your size may have changed over time. Comfort is an important indicator that you have the right size. If you're not sure, hold the cups and watch while you pump. Check the following:

  1. Is the nipple rubbing or sticking against the side of the flange?
  2. Are there skin flakes on the flange after pumping?
  3. Does it feel painful?

If you answered yes to any of the above, you probably need another size. 

You can also hold the flange part on your erect nipple and assess using the diagram below. 

Sizing Inserts

Review the Sizing Guide article to help you find your perfect fit!

The SlimFit Cups come with size 25mm and 28mm Slimfit Fitmie Inserts and a 30mm rigid breast flange to start with. If you need a smaller size, SlimFit Fitmie Inserts are sold separately in packs of (2) and are available in sizes 15mm to 26mm. The 30mm is our largest size.

Bra Fit

If you feel certain you have the right breast flange size, review bra fit and cup positioning here

Pump Compatibility

There are a lot of pump hacks on the Internet that do not work. Use of Freemie SlimFit Cups with a non-compatible pump will not provide consistent results and may result in malfunction. SlimFit Cups are designed to work with a Freemie portable pump, and secondarily, can be used with Spectra S1+, S2+ and P+ pumps only. 

Flange Design

Due to the low profile of the SlimFit Cups, the contour and depth of the flange differs from Freemie Standard Cups and other brands flanges. The Slimfit flange has a slightly flatter slope and bump out flare. Depending on your tissue shape and location of milk ducts, this design variation in design may not work for you. 

Device Health

Your cups need specific care in order to function well. Check the health of your equipment after each use. Look for any tears, holes, cracks, obstructions (such as dried milk) or wear. Remember to replace cup valves every few months. Be sure parts are clean and dry and freshly assembled when you begin a pump session. It is especially important that the cup barriers be checked for tears before and after each use since this important part protects your pump from milk backup.  

Conditioned Response

As with any breast pump product, results can vary. No one product can guarantee a mom's milk supply as every woman's body is unique. Moms all respond differently to different tools. Some moms need to experiment with a lot of different tools and have great difficulty finding the right ones. Other moms easily get their milk with any tool. There are also many hacks and Internet-facts that can help or hinder your efforts. When it comes to the very personal endeavor of lactation and low output, or really any lactation issues, it may be necessary to consult a IBCLC professional or physician. 

It's worth noting that some moms need to watch their milk to have a letdown. Traditional pumping requires moms to hold bottles/flanges while watching their milk ejection reflex. Use of a pumping bra causes bottles/flanges to protrude and/or dangle, and this too is quite a different experience than Freemie's hands-free and concealed pumping tools. With time and practice, it's possible for moms accustomed to traditional hands-on and visible tools to acclimate to wearable pumping, but some moms cannot adjust.

It is important to remember that the release of breast milk is a conditioned response. This means that there are many factors that affect the release of milk. The medical literature has shown that mothers of babies in intensive care units make more milk during or after holding their babies against their skin than when pumping in adjacent rooms, or at home.[2] Stress, fatigue, dehydration, feeling hurried or self-conscious can affect the pumping session. Some breastfeeding professionals recommend bringing a photo of your baby or a piece of clothing from your baby to help stimulate your senses and help your body release your milk while pumping.[3]

“Conditioned responses” may also include factors like the specific rhythm of the pump you have become used to. Different pumps may all pull the same peak amount of vacuum, but their mechanisms can be different. So the pattern of the suction cycles may vary. For two pumps that both measure the same maximum vacuum strength, one’s suction pattern may increase rapidly while the other’s suction pattern may rise more slowly. The Freemie Cups are designed and tested to transmit very similar vacuum as the traditional collection bottles and horns when used with your compatible pump. And the Freemie Pumps pulls up to 280mm-Hg peak vacuum, which also is very similar to the strongest pumps on the market. If you’re changing from one pump setup to another, it may take a little time to get used to the rhythm and suction characteristics of a new pump—or simply the feeling of being hands free with your clothes on—to be able to fully appreciate and benefit from the revolutionary experience of the Freemie system.

Lactation is a very personal endeavor, and only you can decide which tools work best for you. It is important to understand that the Freemie system is just one tool—but it is the tool that is compatible with mothers’ modern day lives. It may not be right for every woman in every setting, every time she is pumping. However, it is certainly the right tool if your circumstances (no time and/or place to undress) would otherwise cause you to skip a much-needed pumping session.

You may worry that you can’t pump around others, because you think you will feel too self-conscious. But let me share a little secret with you; most of the people around you will probably be completely unaware of what is happening. And even if they do know, so what? You have a new baby at home that needs you. Additionally, society is changing. The importance of breast milk is now widely understood. You will probably find that you have the support of your friends, family, and co-workers if you are willing to make the extra effort to continue providing breast milk for your baby, while you also keep up with the rest of your world and do what you need to do.


Mitoulas LR, et al. Effect of Vacuum Profile on Breast Milk Expression Using an Electric Breast Pump J Hum Lact 18(4), 2002.

[2] Acuna-Muga J, et al. Volume of Milk Obtained in Relation to Location and Circumstances of Expression in Mothers of Very Low Birth Weight Infants J of Hum Lact 30(1), 2014

[3] http://www.askdrsears.com/topics/feeding-eating/breastfeeding/while-working/19-tips-better-pumping