Skip to main content Tom's Guide Tom's Guide Search Tom's Guide View Profile Newsletters Best Picks Entertainment Nintendo Switch 2 Microsoft 50th anniversary Best Mattress Wordle Today I put the On Performance Flex Bra through marathon training — here's who should (and shouldn't) buy it Jessica Downey 4 April 2025 Is the On Performance Flex Bra worth $75? We put it to the test. When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works. (Image credit: Future) 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 On On Performance Flex Bra:$75 at on.com If you're looking for a high-quality sports bra that provides medium support, minimizes bounce, and keeps you cool with its sweat-wicking fabric and breathable mesh racerback, the On Performance Flex Bra is well worth considering. First impressions (Image credit: Future) 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. (Image credit: Future) 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. (Image credit: Future) 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 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. More from Tom's Guide Forget weights — this 10-minute bodyweight workout sculpts strong abs I ran 35 miles in the Diadora Gara Carbon 2 — here’s my verdict Best running phone holders Today's best On Performance Flex Bra deals No price informationCheck Amazon We check over 250 million products every day for the best prices Sign up to get the BEST of Tom's Guide direct to your inbox. Get instant access to breaking news, the hottest reviews, great deals and helpful tips. Contact me with news and offers from other Future brandsReceive email from us on behalf of our trusted partners or sponsorsBy submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. Jessica Downey Social Links Navigation Senior Fitness Writer Jessica has been a fitness writer at Tom’s Guide since 2023, bringing three years of experience writing about health, fitness, and the great outdoors. Her passion for exercise began during her childhood, where she spent weekends hiking and competing in local athletics club events. After earning a master’s degree in journalism from Cardiff University, Jessica found the perfect way to combine her love of storytelling and fitness into a career. Jessica is passionate about testing fitness gear and tech, using her reviews to help readers make informed buying decisions. She ran her first marathon in April 2024, finishing it in 3 hours and 48 minutes. Through her training, she’s developed a deep understanding of what it takes to grow as a runner, from effective workouts and recovery techniques to selecting the right gear for every challenge. When she’s not at her desk, Jessica enjoys spending time in the kitchen crafting new recipes, braving cold water swims and hiking. You must confirm your public display name before commenting Please logout and then login again, you will then be prompted to enter your display name. Latest in Fitness Forget planks — use this 8-minute Pilates workout to sculpt your abs and obliques What is osteogenic loading? 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