What *Actually* Happened When I Wore a Period Swimsuit on My Period

Photo: Getty Images/ Juan Algar
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Periods and pool days have never played nice. Wearing a swimsuit borders on risky when I’m menstruating, particularly on heavy flow days. For that reason, I tend to avoid swimming when I’m on my period. However, I was recently introduced to a chic solution: period swimwear. Like period underwear, period swimwear provides the material infrastructure needed to absorb and protect, all while looking chic and pool day-ready.

When I learned Knix, one of the best-selling and most popular period underwear brands, makes a few styles of period-proof swimsuits, I had to get my hands on one. Knix makes its period bathing suits in three different designs: a basic one piece, a one piece with a side tie, and a basic two-piece suit. I tested the Knix Leakproof Side ($100).

knix swimsuit
Knix, Leakproof Side-Tie One Piece Swimsuit — $100.00

Sizes available: XS-XXXXL+

Colors: 3


  • It holds three tampons-worth of blood
  • Beautiful design
  • Easy to wash
  • Lots of stretch
  • Lots of size options


  • Has a compressive fit—size up
  • Expensive

The first time I tested it, I was menstruating, and I wore a tampon—just to be safe. However, toward the end of my cycle (as my flow became lighter), I wore it without any reinforcements.

My honest review of the Knix Leakproof Side-Tie One Piece Swimsuit

The fit

Snatched. That’s how I feel in the Knix one-piece leakproof bathing suit. I can’t lie: The first time I ever tried to put it on, it was a struggle. I’m five feet tall and about 135 pounds, so I got a size small-plus. Firstly, I’d like to note that this is the first brand I’ve seen who offers in-between sizes. Last year I weighed about 150 pounds, so those “schmediums” (the size between small and medium) really come through for me.

knix swimsuit
Photo: Author

While this bathing suit helped sculpt my shape into an hourglass figure, it didn’t do so without a lot of compression on my tummy and ribcage. Truth be told, it was a tad constricting—especially when it came to taking deep breaths. For that reason, I’d suggest getting a size up. When I swam in it, however, it turns out that the same compression made it easier for me to tread through the pool water. Not to mention, it also kept keep my breasts secure and supported.

knix swimsuit
Photo: Author

The function

It’s designed to prevent menstruation leaks from making an appearance on the inside—or back of or front of—your thigh. Menstruators everywhere: rejoice! This leakproof bathing suit works. And it works on multiple levels.

On a mental level, it keeps my anxiety at bay. When I wore this during the second-to-last day I was on my period, I did notice that I worried less about whether I’d have that dreaded red streak creeping down my leg. I could feel myself, erm, leaking, but I could also feel the Knix one-piece absorbing my uterine walls—which effectively prevented any menstrual leaks. I don’t, however, think would handle a super heavy flow. It's designed to be able to effectively absorb three teaspoons of blood, but any more than that (more than about three full tampons), you may experience leakage.

The material

So how does this swimsuit absorb menstrual blood? It features a period-proof gusset made with proprietary FreshFix Technology® fabric (the same material as Knix's period underwear). The gusset is a bit thicker than what a normal swimsuit feels like, although it's not distracting (it doesn't feel like a pad or anything—nor does it look it).

Final thoughts

I hardly spend $100 on anything—but I would spend my own hard-earned cash on this swimsuit. It’s as effective as it is form-fitting, and, as I mentioned before, the brand is wildly size inclusive, carrying up to a XXXXL+. That really makes it stand out from the pack.

Additionally, as someone who doesn’t track her period, the Knix leakproof one-piece actually puts my mind at ease. For instance, if I’m somewhere and unexpectedly get my period, I can rest assured that I won’t live out my teenage nightmare (aka, the surprise of a period starting when I'm near-naked in a pool or at the beach). And that peace of mind is worth $100 to me.

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