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Thinx Period Underwear Review : Testing Out the Thinx Cotton Bikini

Thinx Period Underwear Review

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Updated May 12, 2024

Period underwear has become an increasingly popular option for people with periods looking for a more environmentally-friendly option. Tampons and sanitary pads have been the default choice for decades, but new innovations in textile technology have allowed for a new alternative on the market: Absorbent, yet stylish underwear. Thinx is one of the leaders in this space, and considered one of the best period underwear brands—a company founded in 2013 that focuses on finding a sustainable solution to menstruation and incontinence. Just like standard underwear, these period products come in a range of classic silhouettes: bikini, brief, thong, high-rise, and boyshort. This ensures there’s a fit for every preference, with each style able to hold a different amount of blood. The Thinx for All Cotton Bikini, which I tested and reviewed for this story, is described as being for light-moderate absorbency and able to hold two tampons’ worth of blood. This suggests it’s a good choice for light flows or the last day or two of a period. I put the pair to the test to determine if this is a viable alternative to tampons and other sanitary products. Here are my findings.

Unboxing and first impressions

The Cotton Bikini arrived in a slim clear packet with a cardboard sleeve in vibrant Thinx branding. I was reassured that nothing about the underwear seemed bulky in the package, which had been a primary concern of mine going into this experience. Once unpacked, the black version I received looked similar to standard cotton underwear, with a mid-rise waistline and high-cut legs. The cotton fabric was soft to the touch while still having a nice weight to it. I knew I wouldn’t confuse it with the other pairs in my underwear drawer, without them standing out too much—a perfect balance.

I wouldn’t quite describe these as stylish; the cotton fabric and cut feel a little too simple for that. But they also don’t feel matronly or like underwear for the incontinent elderly, which was my immediate assumption upon hearing “period underwear.” So far, we were off to a good start. 

Pros and cons

As with any purchase, there are a few pros and cons to consider when evaluating whether the Thinx Cotton Bikini is right for you.


  • Fabric choice: The comfortable cotton material is thin enough that it feels comparable to regular underwear, able to fit under clothes, and not be distracting during the day. It is almost a match to a t-shirt bra, if that’s a detail that matters.
  • Size range: Like all Thinx products, this underwear is size inclusive (XS-4X) and available in five colorways for those bold enough to stray away from black.
  • High absorbency: This particular version was labeled “moderate” and was more than sufficient for a full day’s wear. Heavier flows may require a more absorbent pair, but Thinx does sell higher absorbency sets for those customers.
  • Easy cleaning: This underwear can be washed by hand or in the machine on a cold setting and then left to hang dry, which means the set can be easily cleaned and reused within the same cycle.


  • Underwear thickness: While these panties are comfortable to wear, they are noticeably thicker than other pairs and might not be compatible with leggings or other fitted clothing.
  • The “Ick” factor: Simply put, you will be aware that you’re free bleeding when wearing this underwear. For anyone used to pads, this won’t feel different—and is actually an improvement—but tampon-wearers may be uncomfortable for a time.
  • Cost per use: At $17, these are among the cheapest products in the Thinx range ($17-50). But as they’re only for use a few days a month, some might find this a little expensive—even if they work out to be cheaper than other sanitary products over time
  • Potential leakage: Due to the underwear’s fit, there may be a risk of leakage if underwear shifts position and the wearer has a heavy flow.
Thinx for All Cotton Bikini

Thinx for All Cotton Bikini

Thinx period underwear price 

The Thinx for All Cotton Bikini is available for $17 direct from Thinx and can be bundled in sets for additional savings: three to four sets gets you a 10 percent discount, five to six  gets you a 15 percent discount and seven plus gets you 20 percent off. 

Key features

While there’s a lot to like about the Thinx for All Cotton Bikini, there are a few key features that really distinguish itself from other products in the market. 

Three-layered gusset for greater absorbency 

Thinx’s range of period underwear features a three-layered gusset to ensure wearers maintain freshness and dryness throughout the day. There’s a leak-resistant layer that helps retain moisture and forms a barrier with outside clothing, an absorbent layer that holds the liquid released during wear, and a moisture wicking barrier that keeps users comfortable and dry. 

High-cut leg for greater mobility

Thinx understands people on their period may like to engage in some exercise . With this in mind, the Thinx Cotton Bikini is designed with a high-cut leg to promote easier mobility and a larger range of motion. Of course, they’re equally comfortable if you’re not getting active!

Machine washable

The importance of being able to clean period underwear easily and thoroughly should be pretty obvious, which is why Thinx products are all machine-washable on a cold setting. They can also be hand washed, for anyone who doesn’t want to do a full load of laundry each day of their cycle. It’s recommended to hang dry, but I accidentally put mine in the dryer and they came out looking brand new.

Thinx for All Cotton Bikini

Thinx for All Cotton Bikini

How to use Thinx period underwear

The premise of period underwear is that they replace other sanitary products, so theoretically you should be able to wear these just like regular underwear and skip any other precautions. Make sure to check the level of absorbency on the pair you’re using, to avoid any leakage—while some pairs are compared to the equivalence of three tampons, others are closer to one and a half. If you’re wearing a single pair throughout a busy day, you might want to consider bringing additional protection in case your flow is heavier than expected. Make sure to wash each pair after every use. 

How does Thinx period underwear work

Thinx has managed to reinforce standard underwear with additional absorbency, moisture-wicking, and odor control so that they can stand up to a day of menstruating. While the majority of fabric is a simple textile, the gusset uses a three-layered structure for improved performance.

  • The top layer against the skin is moisture-wicking and draws liquid away from the surface for a dry feel throughout the day.
  • The middle layer is absorbent and designed to hold up to five tampons’ worth of blood (different styles offer different absorbencies).
  • The bottom layer is leak-resistant so as to minimize the risk of staining clothes, sheets etc.

As a bonus, most pairs feature a small percentage of elastane in the fabric, for a more comfortable fit in case of any bloating.

My personal experience with Thinx: Do they actually work?

The promise offered by Thinx is appealing—if it holds up. As someone deep into her second decade having periods, I was using tampons as my product of choice and felt resigned to that being the case until menopause. But tampons never quite felt like the best option. As I’ve learned more about the environmental impact of sanitary products, especially tampons with plastic applicators, I began to reconsider how I tackle monthly menstruation. After all, this is something I will likely have to deal with for another two decades at least.

Enter period underwear. On its face, it’s compelling: no added waste, no messing with little packages in the bathroom, nothing inside you at all. But it was also admittedly a little off-putting of an idea at first. While I know using pads isn’t actually “sitting in your own blood,” that is one of the reasons I quickly embraced tampons as soon as possible. The idea of bleeding directly into underwear—especially underwear that would then have contact with my regular clothes—took a real leap of faith. 

Day one 

I should be upfront and say that, as a consistent user of hormonal birth control, my periods have been easier: lasting about 3-4 days, I experience a light to moderate flow and only a little cramping. I know, I’m very lucky. Still, I was nervous to first use the Thinx Bikini when my period arrived. As I pulled them on, they felt just like a slightly bulkier pair of underwear—I was almost concerned with how normal they felt. How could they hold up?

Well, Thinx knows what it’s doing. The bikini underwear was comfortable throughout the day and more than handled the first 12 hours of my period. I initially felt the need to check on things every couple of hours but eventually I relaxed as it became clear this product would uphold its promise for now. After a full day’s wear, I hand-washed them (I don’t have laundry in my building) and hung them to dry, ready for use the next morning. 

Day two

They were dry! Relief. Thinx warns that moderate styles can take about 10-12 hours to dry and I definitely don’t get that much sleep, but my Cotton Bikini was ready for a second wear when I got up the next morning. Day two is usually the worst day of my period for me, so I was a little apprehensive about how they’d perform but also heartened by the previous day’s experience. I told myself that, as I work from home, there was minimal danger of being caught out with a stain, so I put them on and got on with my day.

This was the day I was most confronted with the reality of wearing period underwear. While I never felt wet or uncomfortable, by the end of the day there was definitely a sense of heaviness and dampness that hadn’t been there first thing. When I checked on things, I was able to see that the product was definitely working and that there was no imminent danger of leaks. Still, when I finished the day’s work and proceeded to take a shower, I did still feel the need to spend a little longer getting squeaky clean. The Thinx had done its job but I felt like I’d actually demanded something of it today.

Day three

After lightly hand washing the underwear the night before, I decided that I wouldn’t be comfortable with re-wearing this pair until after a full run in the machine. So I went back to using tampons for Day three and put the period underwear in the laundry. Once they came back, they needed to dry so I was unable to use them again until that night.

The Thinx Bikini isn’t designed specifically for use at night; the brand offers a dedicated Sleep Short for that purpose. However, by the night of Day Three, my period was winding down and I felt comfortable using the underwear as my protection overnight; they had felt secure and stayed in place during the first two days and I’m a pretty immobile sleeper. I didn’t use any additional sanitary products and was pleasantly surprised with how confident I felt when I got into bed that night. Of course, I was asleep for most of the experience but when I did wake up in the night, I wasn’t aware of any wetness or discomfort.

In the morning, I didn’t immediately remember that I was even wearing period underwear; they were that comfortable. I did check the sheets and my pajamas for any possible leaking but was happy to discover the Thinx Bikini had done its job. In fact, the whole thing was so successful that I knew I’d be making this a regular part of my routine.

The rest of the time…

I did wear the Thinx Bikini one more time on the last day of my period, where it more than rose to the task. After its performance on Day two, I knew I’d be in safe hands and didn’t so much as give the underwear a second thought—until I went to pull on some skinny jeans for happy hour and became a bit more aware of the bulkier silhouette. Still, there were no underwear lines visible through the denim. There was minimal discomfort or wetness, but I was still glad to have them as a form of protection.

Ease of cleaning 

As I mentioned earlier, I both hand-washed and machine-washed the underwear during the course of a single period. Both processes left the underwear feeling soft and in-shape, with no visible signs of wear or use. While hand washing is inevitably more effort, it was still pretty easy and fully effective to rid the underwear of any blood or stains. Especially if you’re only washing one pair at a time, this is a minor inconvenience. 

My only frustration came with the drying. Due to the drying timeline of 10-12 hours—and Thinx really recommends you hang dry to ensure they remain elastic and leak-proof over time—I can imagine not always being prepared enough to have them ready first thing in the morning. This would be easily resolved by buying an additional pair, of course.

Thinx period underwear design 

The underwear from Thinx looks comparable to other standard underwear of the same cut, which makes them an easy transition during menstruation. At first glance, you might find it hard to tell them apart, which is a plus for anyone who lives with other people or shares a laundry room or public laundromat. All products are available in black, with different additional colors available depending on the style. Fabrics are a mix of cotton, polyester, polyamide and elastane and every style has the signature three-layered gusset.

The final verdict 

I wasn’t sure what to expect from Thinx period underwear and was inclined to believe they were too good to be true. At best, I thought they’d work but I’d be too uncomfortable to consider making a permanent switch. However, I’ve been pleasantly surprised. There’s no question that the underwear was able to hold up its end of the bargain, although admittedly my period is more moderate than those of many other people. After some initial caution, I grew more confident and comfortable in the Thinx Bikini and quickly stopped checking my reflection in any mirror I passed.

Will I make the full switch from tampons to Thinx? Not quite yet. On lighter days, the ease and freedom from internal products was a huge draw and the slightly bulkier underwear was a happy trade-off for me. Overnight, I loved not having to wear a tampon and being more at ease in the event I overslept – the horror stories about Toxic Shock Syndrome would always linger in my mind and I liked knowing that that would no longer be a concern. However, even though the fabric was able to handle the heaviest day of my period, I felt less comfortable knowing what was going on down there while going about my day. While I hope to grow more relaxed with what is a fully natural phenomenon, admittedly I’m not quite there yet. So I’ll be keeping these as part of my rotation, but mostly for lighter days or as extra coverage with a tampon on heavier days. For me, this feels like a perfect line-up.

Thinx for All Cotton Bikini

Thinx for All Cotton Bikini

Frequently asked questions (FAQs)

Are Thinx period underwear worth it?

For a subjective question, I feel quite confident when I say: Yes! Especially the more affordable products in the cotton range (the bikini, brief and hi-waist are all $17.) When you consider how much money is spent on disposable sanitary products like tampons and pads, this initial investment feels very reasonable. Even if you decide you aren’t ready to completely replace these products with period underwear, using just one to two days a cycle every month will quickly pay dividends. 

Depending on how often you plan to use the period underwear during a cycle—and how much you feel comfortable spending on standard underwear—you may decide that Thinx’s other products (~$34) are also worth it. However, I’d recommend starting with one of these Cotton products to see if it’s the right fit for you.

Do Thinx make you feel dry?

For the vast majority of wear, I didn’t feel any real wetness from the underwear. Thanks to the moisture-wicking technology, it feels similar to how athletic gear can wick sweat from the skin. However, on the heaviest day of my cycle, I was more aware of the blood being collected by the end of the day and did experience some dampness. It wasn’t enough to make me change but it wasn’t particularly pleasant. In the future, I may be tempted to combine the underwear with a tampon during the worst phase of my period to minimize this feeling.

How long can you wear Thinx period underwear?

This differs depending on your particular cycle and flow. When not on your period, the underwear can be worn for a full day just like any standard pair, so the deciding factor is your flow and the product’s absorbency. Thinx provides a guide that compares each style’s absorbency with its equivalent in a sanitary pad or tampon, so that you can have a clearer sense of what your body may need. Those labeled as having super absorbency are the equivalent of five tampons, for instance. On lighter days, I was able to wear the moderately absorbent underwear for 10 hours without any signs of leakage or saturation. 

Thinx for All Cotton Bikini

Thinx for All Cotton Bikini

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