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After years of minimal major improvements to breast pumps,Watch Project Power Online we have come to live in an age of relative abundance. There are now two breast pumps that are big leaps forward for breastfeeding or chestfeeding parents: the Elvieand the Willow.

Both the Elvieand Willoware self-contained breast pumps that are held in place with a full coverage nursing bra. They run on rechargeable batteries – the Willow uses an A/V charger and the Elvie uses USB cables. We've reviewed them both in depth, but here we're putting them head-to-head.

The Elvie is available for purchase either as a single pump or a set of two, while the Willow is only available as a set of two. Since we think most users will opt for the double pump, that's what we'll be comparing in this post.

What's in the box?

The Elvie double pump comes with:

• Two hubs (the motors)

• 4 5-ounce bottles

• 2 24mm breast shields

• 2 28mm breast shields

• 4 valves

• 4 spouts

• 4 seals

• 4 storage lids

• 4 bra adjusters

• 2 USB charging cables

• 2 carry bags

The Willow double pump comes with:

• 2 Willow pumps

• 2 flanges in the size you've selected

• 2 flextubes

• 24 4-ounce milk bags

• 2 cleaning brushes

• 1 charger

This is the first point of differentiation between the Willow and Elvie. The Elvie ships with enough accessories to pump twice without having to wash anything other than the breast shields. This came in handy for me when I needed to pump in the car while traveling; I could just stash the dirty parts in a bag to wash at my destination.

If you're pumping on both sides, you'll need to wash the Willow's parts before using it again, and it can malfunction without regular cleaning.

What are the differences between the Willow and the Elvie breast pump?

The main differences are:

• Cost

• How much milk each can hold

• How active you can be while you pump

• How tricky they are to use

• How you store the milk

Cost

Let's start with money. The Elvie's double pump costs $499 but comes with more parts overall. The Willow also costs $499 and comes with 24 of the company's proprietary bags. Reusable milk containers can be purchased separately for $50, and a package of bags is $23.99 for 48.

If you're pumping with the Elvie, or the Willow's reusable milk container, you can store breast milk in freezer bags, which are available at most stores from brands like Lansinoh or Medela. If you're using the proprietary Willow storage bags, you can buy them directly from the company for $23.99 for a package of 48.

Activity levels

This type of pump allows for greater mobility than standard breast pumps that need to be plugged into a wall and have long tubes connecting the flanges to the motor. They're also more discreet to use. Both the Elvie and Willow are single-user pumps and cannot be shared. Each is eligible to be purchased with money from a health savings account (HSA) or a flexible spending account (FSA). Partial insurance coverage may be available if you contact your insurer.

The Willow seems to have the clear edge in terms of what activities you can do while pumping, thanks to the one-way valve in the bag. Wearing a snug bra keeps the Willow secure enough to do yoga or other moderate-intensity activities, even where the pump becomes inverted or when the user is lying down. This is an engineering achievement on its own.

Wearing the Elvie didn't feel nearly secure enough to try exercise or significant moving around while pumping. I didn't want to risk disrupting the seal and having to start over.

Milk volume

The Elvie can handle a greater volume of milk produced in a session – 5 ounces compared to 4 ounces for the Willow. The Willow shuts off automatically when it senses that it's full. This is a needed feature since you can't see how much milk is in the bag while you're pumping. However, it’s also possible for the pump to shut off prematurely if the sensor is wrong.

In contrast, the Elvie's milk bottle is underneath the motor and visible from the outside, though your bra will be covering it while you pump.

Tips and tricks

The Elvie comes with two sizes of flanges in the box. The Willow is sized, so you need to measure your breast before purchase and choose the option that should fit. If you measure wrong, you'll need to order a new part.

Choosing between the Willow and the Elvie will probably come down to which features matter more to you, though knowing that in advance may be tricky for someone attempting to pump or breastfeed for the first time. The Willow can be challenging to put together for the first time, and it has a Flip to Finish maneuver that moves all the milk into the bag at the end of a session. Our reviewer found this took a bit of practice, and she accidentally dumped milk all over her counter the first time she did it.

Here's what a day with the breast pumps looked like...

With any pumping session, you'll pump breast milk into either a bottle or a bag, depending on your pump, and then either give it to your baby immediately or store it for later use. If the baby is drinking all the pumped milk within a 24-hour period, then keeping the milk in bottles in the fridge will probably be the easiest choice. Many moms pump a stash of milk prior to returning to work and freeze it. In those cases, the baby may drink milk that's been defrosted and the newly-pumped milk will be frozen until it's used.

This distinction matters because it affects what kind of milk storage you might prefer.

The Willow can pump breast milk directly into its proprietary bag, which is freezer-safe. Thanks to a one-way valve, you also can't spill it at this stage. Unfortunately, Willow's bags are more expensive than standard breast milk bags you can buy from a grocery store or pharmacy. And if you're using the breast milk without freezing it, you'd use a disposable bag every time.

The Willow does have an option to buy a reusable plastic milk container that attaches to the pump. You can pump into the reusable milk container and then pour the milk into any bag you want before you freeze it. However, one set of reusable containers costs $50, and you can't pump without them. You'll need to wash them and store the milk in a second container to keep pumping.

If a typical day in the office (post-pandemic, hear me out) would require 2-3 pumping sessions, you'll need to bring another container with you to store the milk, or dump it into storage bags.

In contrast, the Elvie comes with four bottles, which goes farther than you think. The total 5-ounce capacity was enough to hold an entire pumping session's worth of breast milk. So a three session day might look like this:

• Session 1: Pump with bottles 1 and 2, then combine it all into bottle 1 and wash bottle 2.

• Session 2: Pump with bottles 3 and 4, then combine it all into bottle 3 and wash bottle 4.

• Session 3: Pump with bottles 2 and 4, then combine it into bottle 2.

So at the end of the day you'd have three bottles of milk and one more to wash. Alternatively, you could use bottles 1 and 2 for Session 1, then combine it into a freezer bag and wash the bottles. For session 2, you'd repeat the process with bottles 3 and 4, and then use the now-dry bottles 1 and 2 again for the last session of the day.

The extra bottles that come with the Elvie create more flexibility in terms of milk storage options, and I didn't have to do as much cleaning right away. Both the Elvie and Willow work best when all the parts are dry, so the extra drying time afforded by the second set of parts was helpful.

If the user isn't storing the milk, but just pumping to feed their baby shortly afterward, then the bag innovations of the Willow don't pay off, making the Elvie easier to deal with.

– Katherine J. Igoe contributed reporting