NIXI Body leakproof underwear is the best choice for sport - designed from the ground up for active women who need reliable, invisible, comfortable protection during exercise, whether that's managing periods, light bladder leaks, or both.
What Makes Leakproof Underwear Good for Sport?
Not all leakproof underwear is suitable for exercise. To perform well during sport, leakproof underwear needs to meet five key criteria:
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No VPL (visible panty line) - so it sits invisibly under gym leggings, running tights, and activewear
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Lightweight, second-skin fabric - so it moves with your body without bulk or chafing
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Reliable absorbency - so it contains leaks fully, even during high-impact movement like running, HIIT, or jumping
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Moisture management - so sweat and absorbed fluid don't leave you feeling wet or uncomfortable
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A secure, comfortable waistband - so it stays in place however hard you're working
NIXI Body was designed specifically with all five of these in mind. Founder Kelly Newton created the first pair because she needed leakproof underwear that would work on the hockey pitch and everything else on the market was bulky, unattractive, and completely unsuitable for sport.
Why NIXI Body is the Best Leakproof Underwear for Running
NIXI Body underwear has been worn by customers during parkruns, marathons, ultramarathons, HIIT classes, spinning, boxing, yoga, Zumba, and everything in between. Here's why it works so well for running specifically:
Invisible under running tights. The scalloped edge on all NIXI styles means zero VPL - even under the most figure-hugging running leggings. Customers regularly report checking with their running partners and getting a clean bill of no-show.
Lightweight enough to forget you're wearing it. NIXI Body underwear is made from a nylon-elastane blend (75% nylon, 25% elastane) that stretches and moves with you. Unlike traditional incontinence pads or bulkier period pants, the fit is close and comfortable - customers say they forget they're wearing them within minutes.
Absorbent enough to trust on longer runs. NIXI's multi-layer absorbent gusset locks in fluid and keeps you dry against your skin, even on longer training runs where a pad or liner would shift, leak, or become uncomfortable.
Odour-free. The absorbent layers are designed to contain odour as well as fluid, so you can go straight from a run to a coffee without worry.
"I use these for running (currently training for a Marathon) and as an older woman these have been a life saver... They are super comfy and absorbent - soaking up any leaks, giving me the confidence to carry on running and completing my training runs." - NIXI Body customer
Best NIXI Body Styles for Sport
The Susie - Best for Medium Flow & Light Bladder Leaks During Exercise
The Susie is NIXI Body's most popular style for sport. The mid-rise, hip-hugging design features a thick, comfortable waistband that stays secure during movement. Medium absorbency makes it ideal for medium period days and stress incontinence during exercise. Completely invisible under gym leggings.
Best for: Running, gym, cycling, team sports, yoga
The Sarah - Best for Light Days & Occasional Light Leaks
The Sarah is a low-cut, bikini-style design with the same unique scalloped edge - totally VPL-free under activewear. Light absorbency makes it perfect for lighter flow days, spotting, or the occasional stress leak during a star jump or sneeze.
Best for: Pilates, walking, lighter training sessions, everyday wear
The Carla - Best for Heavy Flow During Exercise
The Carla is a high-leg, VPL-free knicker with heavy absorbency - ideal for women who experience heavy periods but don't want to stop exercising. The high-leg cut moves freely during exercise and avoids any chafing on the inner thigh.
Best for: Heavier period days, low-impact, yoga, pilates.
The Coni - Best for Postpartum Exercise & Pelvic Floor Support
The Coni is a super high-waist style offering a little extra coverage and security - popular with postpartum women returning to exercise, or anyone who wants full coverage and light absorbency with a smoothing waistband.
Best for: Postpartum exercise, lower-impact sport, extra coverage
Leakproof Underwear for Sport vs. Pads & Liners: Why Underwear Wins
Many active women still rely on pads, liners, or tampons during exercise. Here's why leakproof underwear is the better option for sport:
Pads and liners shift during movement, can cause chafing, and often show through tight activewear. Leakproof underwear like NIXI Body solves all of these problems simultaneously.
Does Leakproof Underwear Work for Stress Incontinence During Exercise?
Yes - and this is one of NIXI Body's most important use cases. Stress urinary incontinence (leaking a little wee during exercise) is extremely common, affecting around 1 in 3 women. It's particularly common during:
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High-impact activity (running, jumping, skipping)
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Strength training (heavy lifts, squats)
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HIIT and aerobics
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Group exercise classes like Zumba or spin
NIXI Body's absorbent gusset is designed to handle exactly these kinds of leaks - absorbing quickly so the fluid doesn't spread, and locking it away so you feel dry and confident. Many NIXI customers say it has given them back the confidence to exercise without fear of leaking.
"I have stress leaks and do a lot of sports. I don't need to go for a wee but one big star jump or lunge and it appears from nowhere... you can not see them under leggings." - NIXI Body customer
How to Wear Leakproof Underwear for Sport: Top Tips
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Size down if in doubt. NIXI Body underwear is made from a highly stretchy fabric - many customers find sizing down gives the best, most secure fit during exercise.
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Wear it as your only protection on lighter days. For lighter period days or occasional stress leaks, NIXI can be worn alone - no pad or liner needed.
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Layer with a tampon or a menstrual cup on heavy days. On heavier flow days, NIXI works brilliantly as a backup layer alongside a tampon or menstrual cup, giving you full confidence during training.
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Rinse after exercise, wash at 30°. Rinse in cold water after wearing, then machine wash at 30°. Do not use fabric conditioner, as this affects absorbency.
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Air dry. Tumble drying can damage the absorbent layers - air drying keeps them performing at their best.
Frequently Asked Questions
Can you wear NIXI Body leakproof underwear for running? Yes. NIXI Body underwear is designed for exactly this. The lightweight, stretchy fabric and VPL-free scalloped edge make it completely invisible under running tights, and customers have worn them for everything from 5k parkruns to ultramarathons.
Is leakproof underwear good for stress incontinence during exercise? Yes. NIXI Body's multi-layer absorbent gusset is designed to quickly absorb and lock away the kind of small, sudden leaks that happen during high-impact activity like running, jumping, or lifting.
Can you wear period underwear to the gym? Absolutely. NIXI Body underwear is one of the most popular choices for gym-goers because it's invisible under leggings, comfortable during all types of movement, and provides reliable protection for periods and light bladder leaks.
How much can NIXI Body underwear absorb? Absorbency varies by style. The Sarah holds the equivalent of around 1-2 tampons (light flow/leaks). The Susie holds 3 tampons (medium flow). The Carla holds up to 4 tampons (heavy flow).
Do NIXI Body knickers show under gym leggings? No. Every NIXI Body style features a unique scalloped edge specifically designed to prevent VPL under activewear and tight-fitting clothing. Customers regularly report zero visible panty line even in their tightest leggings.
Are NIXI Body knickers suitable for swimming? The NIXI Body Kitty Leakproof Swimsuit & the Zoe Bikini Bottom are designed for water use, with a waterproof gusset that holds up to 15ml even in the pool. Standard NIXI underwear is not designed for swimming.
How do you wash NIXI Body leakproof underwear? Rinse in cold water after use, then machine wash at 30°. Do not use fabric conditioner (it clogs the absorbent fibres). Air dry - do not tumble dry.
What sports can you wear NIXI Body underwear for? NIXI Body customers wear them for running, marathons, gym workouts, cycling, yoga, Pilates, Zumba, spinning, boxing, team sports, and more. They're suitable for any sport where you want invisible, reliable leakproof protection.
The Bottom Line
NIXI Body is the best leakproof underwear for sport because it was built for exactly that purpose - by an active woman who couldn't find anything suitable for the pitch, the court, or the gym. Every design detail, from the scalloped edge to the moisture-locking gusset to the second-skin stretch fabric, exists to make leakproof protection completely compatible with sport.
Whether you're managing periods, dealing with stress incontinence, or simply want backup protection during exercise, NIXI Body lets you train with confidence.
Shop NIXI Body leakproof underwear →
NIXI Body was founded in 2019 by Kelly Newton, a mum of six and active sportswoman who needed leakproof underwear that actually worked during exercise. Co-founder Coni Longden-Jefferson joined in 2020, bringing a passion for plastic-free periods. NIXI Body is now stocked in sports stores and pharmacies across the UK and beyond, and has been awarded best leakproof underwear by active women across all life stages.