Finding the right sports bra for running is tough. Too loose, and there’s not enough support; too tight, and you risk discomfort, restricting your movement, rubbing and even painful chafing.
So when I started testing the On Performance Flex Bra during my marathon training, I wanted to see if this $75 sports bra could handle long-distance runs, sweaty conditions, and frequent washing without compromising on comfort.
Over the past month, I’ve put this bra through 56 kilometers of running and a few strength workouts. Now, as race day approaches, here’s how the On Performance Flex Bra performed, and whether it’s worth the price tag
First impressions
When I first put the Performance Flex Bra on, I had mixed feelings. The straps looked notably thick, and I worried they might dig into my shoulders. But they turned out to be surprisingly light and comfortable. The straps are also adjustable, which is a great feature in a sports bra as it allows for a more customized fit.
The material felt soft and breathable, and the racerback cutout was a good indication that the bra offers plenty of ventilation. On the hanger, I initially thought the cups looked very protruding, and I wasn’t sure how they’d sit once worn. However, once on, the cups molded to my chest and didn't hold any weird shape, which was a relief.
The bra was also easy to take on and off, which, let’s be real, is a godsend after a long workout. There’s nothing more annoying than struggling to wrestle off a wet sports bra after a sweaty session.
Fit, feel, and durability
The high neckline provides great front coverage and support, which is a bonus for running and high-intensity workouts. The size small I tested fit well from the front, but if I had to nitpick, I was a touch more conscious of how it fit and looked at the back.
I tend to run and work out in just a sports bra because I hate feeling too hot while exercising. But, I did feel a little more aware of how much skin was on show and the cut around the cutout, with it perhaps being a little tight for me at the back. That said, since I was doing a lot of long training runs in this bra, I often had one of the best hydration packs covering the back.
My main reason for mentioning this about the fit is that the size small fit me well at the front, so sizing up could have compromised the support I felt in the chest area at the front.
Enough about sizing. The built-in padding in the On Performance Flex Bra is light and non-intrusive, and I was impressed by how well the shape held up after repeated washes, something many budget bras fail at.
One of the biggest perks I found while testing this sports bra is its sweat-wicking abilities. Unlike cheaper sports bras I own, which absorb sweat and feel unpleasantly wet after a session, the Performance Flex Bra dries quickly. This is a huge plus for anyone logging high mileage, I didn’t feel gross during or after my runs, which makes a difference.
Performance
As mentioned earlier, I wore the Performance Flex Bra for a few strength workouts, but the bra spent a lot of time on me as I ran, training for the London Marathon. So, I will mostly be referring to how this felt while running a mix of distances and at different intensities.
For me, a sign of a great sports bra is that you don’t think about it while running, and the Performance Flex bra ticked this box for me. I didn’t think about it while running, whereas I’ve worn my fair share of lesser quality sports bras that have me feeling very uncomfortable up top, where the bra feels restrictive or digs in and rubs.
Over multiple runs, including a sweaty 32km session in 62°F London Spring sunshine, this bra stayed secure, comfortable, and chafe-free. That’s impressive, considering how much heat and sweat can build up and cause irritation during long-distance training. This sports bra is a medium support bra, and I'd say it lived up to this. It didn't feel overly compressive, but I felt adequately supported as I ran.
I also noted the level of breathability the bra had to offer. The combination of a good quality sweat-wicking fabric, a mesh racerback panel and the cutout — which I ended up being grateful for — meant that even after long, hot runs, the bra felt light and dry rather than heavy and damp. This is a big upgrade from cheaper sports bras I’ve relied on in the past, which feel soaked and uncomfortable post-run.
Who should (and shouldn’t) buy it?
Buy if you:
- Are happy to spend more on a sports bra
- Need a supportive sports bra for running or high-intensity workouts
- Want breathable, sweat-wicking fabric that stays light and dry
- Prefer built-in padding
Skip if you:
- Want a budget-friendly sports bra
- Prefer higher or lower support (this is a medium support sports bra)
- Like a lower neckline
Verdict
After a month of testing, I’m definitely impressed with the On Performance Flex Bra, especially when it comes to comfort and sweat-wicking performance.
That said, the price is on the steeper side for such a small piece of material, and the style won’t be for everyone. But if you’re looking for a high-quality running bra that stays comfortable and chafe-free during tough workouts, it’s definitely worth considering.
I can’t fully comment on its long-term durability just yet, as I’ve only had the On Performance Flex Bra for a month. If it continues to hold its shape, doesn’t pill, and handles sweat as well as it has so far, I think the On Performance Flex Bra is worth the investment if you are happy to spend over $70 on a sports bra.
If you don't want to part ways with that kind of money, check out our guide to the best sports bras to find more affordable alternatives on the market.
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