How Does Period Underwear Work?


Period panties might be new to you. So, when you’re looking into period undies you’re likely to wonder: How do they work? 

Good question! You may feel like there’s some impossible witchcraft going on, but these undies are the next evolution in feminine hygiene. But before we get into how it all works, let’s take a look at just how far we’ve come...

Then & Now: A History of Menstrual Management

Then: The Same Old Stigmas

For many decades, methods of managing menstruation went unchanged, with pads and tampons being the main products used.

Although they continued to evolve, tampons went on the market in the 1940s. After the introduction of adhesive pads in the late 1960s, innovation pretty much stopped.

This is shocking when you consider half of the world’s population menstruates. But when you also consider how taboo menstruation has been until very recent times, it’s not altogether surprising.

Now: Innovative New Products Like Period Underwear

Thankfully, we finally feel like those times are behind us. There are definitely interesting innovations hitting the market when it comes to menstruation. And period undies are by far one of the most exciting (and sustainable!)

But after years of using the same period products and solutions, it can be difficult to make a change. It’s important to all of us to trust the menstrual protection we choose. So, if you’re contemplating trying leakproof undies, it’s a natural question: How the hell do they work?! 

How Do Period Undies Work?

There are different brands of period undies on the market and they’re all designed slightly differently, with their own styles and innovations.

The secret design of the technical fabric used to make these panties are kept under tight wraps by these companies. 

The Secret to Period Panties Is in the Fabric Layers

When people first encounter period underwear, they often expect bulky undies. It can be a little head-wrecking to imagine these thin, wearable, and (yes!) cute panties doing a good job absorbing menstrual blood.

The secret design of the technical fabric used to make period panties work is kept under tight wraps by these companies.

For example, in Knix underwear, there are three hard-working layers that make period panties work. 

The patented technology built into Knix underwear locks in moisture, helps get rid of odor and stops leaks. Designed to be both safe and effective, it’s 100% free from PFAS and is OEKO-TEX® certified.

  1. Moisture Wicking, Anti-Odor Cotton Layer: Cotton is a natural and breathable fabric. It wicks away moisture and is anti-odor so you can be confident all day long. 
  2. Polyester Super-Absorbent Fabric Layer: Fresh Fix Technology® makes a wicking polyester layer that absorbs and traps moisture, blood, leaks, and/or sweat. 
  3. Polyester Leak-Resistant Layer: This waterproof membrane helps prevent leaks and keeps you feeling confident. If this were an old tampon commercial, you’d see a woman in white pants right about now ;)

Knix’s Leakproof Undies act like a barely-there built-in panty liner. They can absorb as much liquid as 12 regular tampons (12 tsp of blood), depending on style. They will feel slightly different than your regular underwear but without the bulk of a large pad. 

We recommend using leakproof products as your only period management product or as backup leak protection used in conjunction with menstrual cups, pads or tampons… basically whatever you’re most comfortable with.

Not All Period Underwear is The Same

Just like tampons and pads, period panties come in a variety of styles. The technology can differ from brand to brand. So spend some time looking at the individual specifications of any undies you’re considering purchasing.

Nobody knows your period better than you. Whether you have a light flow or heavy flow, use period underwear as your only solution or in conjunction with other products… it’s your choice. You may even make different decisions for different days of your cycle, like on heavy flow days.

Even though our super leakproof underwear can absorb 8-12 tsp of blood (or 3-4 tampons worth), some people experience exceptionally heavy menstrual flow, clotting, or ‘flooding’. For some, then, period underwear serves best as a back-up on heavier days or overnight. But for the majority, it’s all you need.

It may take some time to find your perfect solution. But regardless of your flow, period undies can definitely lend a helping hand!

Okay… But Why Are Period Undies Better?

There are many compelling reasons to consider using period undies.

Comfort & Confidence 💃

Period underwear won’t force you to compromise on comfort or style. In fact, they can be comfortable and pretty! You don’t need to resort to wearing those ratty old panties that you’re okay with staining. 

On lighter days, period underwear can liberate you from panty-liners. It’s also worth noting that insertables (like tampons) aren’t comfortable for everyone. So period undies open up another option.

This confidence is especially needed for teens who are still getting used to their period and flow. They may also be in class or at camp for longer periods without bathroom breaks. 

Moreover, familiar realities for older women like blood-stained sheets can be embarrassing for teens who have to deal with parents. So the protection offered by period underwear helps them not only with the logistics of period management but helps offset accompanying anxiety too.

Save Some 💰

Feminine hygiene products are not cheap and many simply cannot afford them (it’s known as period poverty). It’s exciting to think how period undies could revolutionize periods for women worldwide. Especially those who may not have access to, or be able to afford, expensive disposable products.

Let’s face it: None of us are daydreaming about the tampons on our monthly shopping list! Those saved dollars can definitely add up!

Helping the Planet! 🌎

Sustainability is something we all want to improve. Whether you’ve eliminated plastic straws or upped the ante on recycling, most of us are continually looking for ways to reduce waste.

Whether you use pads or regular tampons, applicators or not, periods can create a lot of waste. Even if you don’t wholly eliminate tampons or pads, using them on fewer days will have a positive impact on our environment.

Your Period, Your Choice 💪

In general, more choice is better. Period underwear and other alternative periods products have broken the ‘dry spell’ of innovation in period products. 

This creates more choice, which empowers people with periods, young and old. But it also means there’s more discussion about periods, period health and products. This is going a long way to decreasing the stigma and shame that surrounded periods for so long.

For instance, did you know that the modern style menstrual cup first emerged in the 1930s but there was low adoption because women were too squeamish about coming into close contact with their bodies and their own menstrual blood? That’s part of the reason tampons with applicators were such a hit when they emerged.

So that there’s appetite and interest for products like the menstrual cup and period underwear is a sure sign that we’ve become more open and accepting of these conversations and experiences. And this will lead to women being more in touch with their entire cycle, and confident to judge something’s not right.

How Long Can You Wear Period Underwear? 

You can wear period underwear all day, every day (whether you’re on your period or not). Many women love their Knix so much they replace all their undies! They’re great for all of life’s little leaks. 

But there are limits on how much different styles of period underwear can absorb. 

What Absorbency is Right for Me?

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Knix Product

1-3 tsp 


4-8 tsp 

Super Leakproof

10 tsp 

Cotton Super Leakproof Boxer Brief

12 tsp 

Super Leakproof Dream Short & Reusable Pads - Regular

20 tsp 

Reusable Pads - Overnight

For example, Knix Leakproof Underwear absorbs 3 tsp of liquid, which is more than a regular tampon’s worth of blood (a soaked normal-sized tampon or pad holds a teaspoon or 5ml of blood).  This makes Leakproof Underwear ideal for light days or as a backup solution on heavy days. 

But if you're looking for extra protection, check out the Super Leakproof range for absorbency up to 8 tsps.

For even heavier flow, or overnight there’s the Super Leakproof Boxer Brief and Super Leakproof Dream Short (10-12 tsps).

How Do You Wash Period Underwear?

It’s natural to think that such technical undies will require special care. A lot of lingerie is “hand wash only”. But period underwear isn’t necessarily so fussy.

Again, different manufacturers will have different care instructions. And it’s definitely worth paying attention when you’re making a choice. After all, nobody wants to get home and realize they’ve got some high-maintenance undies on their hands!

Knix Leakproof Underwear is as low maintenance as it gets. You simply machine wash them on a cold water cycle, with mild detergent. We advise against using bleach and then laying flat to dry.

It’s important to note that undies are not completely stain-proof! So, we also recommend giving them a quick rinse before tossing them in the washing machine.

Ready to Try?!

If you’re ready to try Leakproof Underwear, check out our selection here.

The patented technology built into our underwear locks in moisture, helps get rid of odor, and stops leaks. Designed to be both safe and effective, it’s 100% free from PFAS and is OEKO-TEX® certified.

Leakproof undies are perfect for people who experience light bladder leaks, wear panty liners on a regular basis, or are concerned about excess sweating. Just wear, wash, and repeat, and you’ll have one less thing to worry about!

Updated on November 1, 2021.