Frequently Asked Questions

Orders & Shipping

I’ve already submitted my order, but I need to make a change! What do I do? Is it too late?

We process our orders quickly (so you can get your undies in a jiff), but we will do our best to accommodate any requests you may have. The best way to adjust or cancel an order is to email or call us at (917) 819-8171.

How long will I wait for my underwear after I submit my order?

Your order should ship within 1-2 business days (Mon-Fri, before 5pm), and arrive within 5-7 business days if you select standard shipping, or 1-3 business days with expedited shipping (continental US)––unless you've pre-ordered something, in which case the shipping date will be indicated upon placing your order.

What is your return policy?

Not loving your undies? No worries — we process returns and exchanges within 60 days of purchase, no questions asked (not valid on final sale items, tampons, merch, or gift cards). We will also provide you with a free pre-paid return label. You can request a return or exchange via

If your order qualifies for a return, more

I live abroad. Can I still order Thinx (BTWN)?

Yes! We offer international shipping so everybody can have the most innovative period solutions.

Does Thinx (BTWN) cover taxes, duty, etc. for international customers?

Unfortunately, our prices don't include local taxes, duties, brokerage fees, VATs, or any other stuff you may be additionally charged to receive your Thinx (BTWN) shipment internationally.

Make sure you consider *all fees* before you place your order because you’ll be required to make those payments when your shipment arrives, and we won’t be able to refund you if you change your mind.

What currencies do you accept?

We *love* our friends from all around the world, which is why we accept nearly all local currencies. On the off chance we do not accept your local currency, you’ll have the option of checking out in USD, CAD, EUR, AUD, or British Pounds.

I'm having trouble placing my order on your website. Help!

While we do our best to ensure that our e-commerce experience is consistent, enjoyable, and functional across all modern browsers and devices, occasionally something small may not function properly on older browsers when an update to our code is pushed.

If you are having trouble logging in, creating an more

What is a Custom Set and how do I get it?

When you shop Thinx and Thinx (BTWN), you can combine your purchase to receive our Custom Set discount: buy 3 - 4 pairs and save 10%, buy 5 - 6 pairs and save 15%, Buy 7+ pairs from any brand and save 20%. This way, teens *and* moms (or aunties/big sisters/cousins) can period better and save $$$. FYI, Fresh Start Period Kits are not eligible for a Custom Set discount.

Can I return or exchange one or two pairs of underwear from the Fresh Start Period Kit?

The Fresh Start Period Kit is sold as a unit, so you can't return or exchange individual pairs of undies from it, but you can return or exchange the whole kit, no questions asked.

What type of payment is accepted?

We are a cash-free establishment, and accept all major credit cards. Thinx gift cards can only be used for online purchases.

Are undies I buy at the pop-up store final sale?

Nope, unopened and unworn merchandise purchased from our pop-up can be returned or exchanged in store. If you’d like to return items you purchased items online, email


How do Thinx (BTWN) work?

Every pair of Thinx (BTWN) is made with period-proof technology to keep you fresh ‘n’ dry: moisture-wicking cotton, an odor-trapping lining, super-absorbent fabric, and a leak-resistant barrier.

Check out our Product Info page to—you guessed it—learn more about how Thinx (BTWN) work!

And if you want to learn more about how *periods* work, we’ve got a page for that, too.

How much liquid can Thinx (BTWN) hold?

Each pair of undies holds at least 17 mL of fluid.

How long can I wear Thinx (BTWN)?

For most tweens and teens, our undies can last between 4 - 6 hours. But every period is different, and depending on your flow (light, medium, heavy) you may have to change your Thinx (BTWN) more often (pro tip: if you have a long day ahead of you, pack extra pairs). We *always* suggest you try Thinx (BTWN) at home first to understand how it works for your body and your period.

What if I need to change my Thinx (BTWN) during the day?

Depending on your flow, you may need to pack an extra pair of Thinx (BTWN) to get through the day — no big deal! Our undies are lightweight and easy to store, so an extra pair will fit perfectly in your backpack or gym bag. We suggest bringing a resealable bag or pouch so that when you do need to change out of your first pair of Thinx (BTWN), you’ve got a place to put it. Just don’t forget to wash *both* pairs when you get home!

Will there be stains on my Thinx (BTWN)?

Nope. The interior of Thinx (BTWN) is lined with black fabric, so you never look down and see stains.

Are Thinx (BTWN) reusable?

You bet. Our period-proof underwear are washable and reusable. Plus, they’re easy to take care of and can last up to 2 years.

Are Thinx (BTWN) a replacement for my current routine?

Depending on your flow (light, medium, heavy), Thinx (BTWN) can be worn alone or with other period products. On your light days, wear the undies instead of pads and panty liners. On your heavy days, wear ‘em as a backup to other products for extra protection. We *always* suggest you try Thinx (BTWN) at home first to understand how it works for your body and your period.

Every person and every period is unique. Over time you’ll get to know yourself and your flow better—and we’ll have your back while you figure it out.

Can I wear Thinx (BTWN) as a backup to pads and panty liners?

No. Thinx (BTWN) are designed to fit close to your body to help prevent leaks and stains. If you put a pad or panty liner on top of your Thinx (BTWN), our special technology won’t be close enough to your body to absorb your period. If you usually wear pads and panty liners, try wearing 1 or 2 pairs of Thinx (BTWN) throughout the day instead — without anything else. If you like to wear tampons, you can wear Thinx (BTWN) with as a backup (because tampons sit inside of you, our undies will be close enough to your body to help prevent leaks).

How can you be sure they won’t leak?

Our signature period-proof tech has been tested by product developers, doctors, and real people just like you — Thinx (BTWN) really does work! But every person and every period is unique, so it’s important to know your flow to better understand how Thinx (BTWN) can work for you. Some people with heavy flows wear the undies as a backup to other period products, and some people with light flows wear them instead of pads and panty liners. We suggest trying them at home first to figure out what’s best for you.

How many pairs of Thinx (BTWN) do I need?

Some people buy a Fresh Start Period Kit so they have multiple pairs ready to change into, while other people start with just one pair and wash it at night before wearing the next day. It’s up to you and how often you want to wear and wash your Thinx (BTWN). (Insider tip: You save $$$ if you buy a Fresh Start Period Kit!)

How do I know which Thinx (BTWN) is the right size for me?

Our undies are true to classic sizing for girls’ underwear and clothing. Take a peek at our handy sizing chart to get the right measurements for the perfect fit.

Are Thinx (BTWN) hygienic?

Yes! Every pair of underwear is lined with odor-trapping technology to keep you fresh ‘n’ dry, not to mention super-absorbent and moisture-wicking materials so you never feel like you’re sitting in a diaper (ew).

How do Thinx (BTWN) control odor?

The wicking layer of our signature period-proof technology has an application of non-migratory silver, commonly used in performance wear and medical devices to control odor and the spread of bacteria. “Non-migratory” means it won’t come off your undies and that it only responds to bacteria *on the fabric*, not on your skin (so your vaginal microbiome stays fresh and balanced!).

How do I wash the underwear?

We recommend that you rinse them by hand after use, and then throw ‘em in the wash with the rest of your laundry (cold or warm). Finally, hang dry.

DO NOT use fabric softener, bleach, or irons, as they hurt the period-proof technology!

Can I wear Thinx (BTWN) as a swimsuit?

We don’t recommend wearing these undies as a swimsuit because we can’t guarantee the technology will work in the water.

I have sensitive skin — what are Thinx (BTWN) made of?

The entire gusset is lined with cotton so you have a natural fiber touching your most sensitive area. And the body of each pair of Thinx (BTWN) is made of organic cotton, which is super-cozy and extra-breathable. Here’s the fabric breakdown: outer shell: 95% organic cotton, 5% elastane; inner lining: 95% organic cotton, 5% elastane; middle layers: 95% cotton, 5% elastane, 80% polyester, 20% nylon, breathable.

Where are Thinx (BTWN) manufactured?

Our undies are made by our partners at MAS, a family-run factory in Sri Lanka known for their expertise with intimates. We’re proud to work together because they share the same values we do: empowering women and creating innovative, sustainable period solutions.

Where can I buy Thinx (BTWN)?

Right here! We currently sell our undies exclusively online. Shop all our Thinx (BTWN) styles here.

Why do Thinx (BTWN) cost more than pads and tampons?

Our undies are washable, reusable, and made with period-proof technology — there’s *a lot* of science and development that goes into making them, and making sure they last. Disposable products can only be used one time, but Thinx (BTWN) can last up to 2 years — that means over time you can save serious $$$.

What are Thinx?

Thinx are period-proof underwear made for adults. Both Thinx and Thinx (BTWN) are made with four layers of special technology—moisture-wicking cotton, odor-trapping lining, super-absorbent fabric, leak-resistant barrier—to help prevent leaks, stains, and smells. Thinx styles are made with taller, curvier adult bodies in mind.

How do Thinx (BTWN) compare to the original Thinx line?

Thinx (BTWN) are made with the same period-proof technology as our Thinx underwear line, but specially designed for younger bodies and first and early periods. This means that Thinx (BTWN) are made to fit teen and tween bodies with snugger leg holes, a narrower gusset, and straighter hips. And while Thinx come in a range of absorbency levels, every Thinx (BTWN) style is made with our highest absorbency (holding up to 3 teaspoons’ worth of fluid, or 17 mL) so tweens and teens can get to know their flows without worrying about leaks and stains.

What if I fit both Thinx (BTWN) and Thinx?

Thinx (BTWN) are made for teen and tween body shapes and sizes. Thinx are engineered for adult bodies. If you need help deciding which line is right for you, drop us a note and we’ll help you find the *perfect* fit.

Do Thinx (BTWN) and Thinx have the same absorbency levels?

While Thinx styles offer a variety of absorbency levels, all Thinx (BTWN) styles provide maximum absorbency. Why? Because tweens and teens live busy, full lives, and first and early periods can be inconsistent and uneven. This high-level absorption helps reduce worry about leaks and stains.

What's the difference between Thinx (BTWN) and Thinx styles?

All Thinx (BTWN) undies are full-coverage, provide maximum absorbency, and are specifically designed for tween and teen body shapes and sizes. Thinx offers a range of styles for adults — from super-comfy boy shorts to barely-there thongs — with different levels of absorbencies. See all our Thinx (BTWN) styles to choose what’s right for you.

Period Info

What exactly is a period, and why do I have one?

The simplest explanation is that a period is when your body releases blood and tissue that it no longer needs through your cervix and vagina. This tissue is a lining in your uterus (where an egg travels from your ovaries during ovulation) that gets thicker in preparation for the egg to be fertilized. When you don’t become pregnant, your body releases both the lining and the unfertilized egg approximately every 21 - 45 days. This is menstruation, or what we call “a period,” and it’s totally natural!

When will I get my period?

Every body is different, and it’s no big deal to get your period before or after your friends. Some people get their first period as early as 8 or 9 years old, others get them as late as 16. First periods often happen around the same time in life for people who are related to one another, so ask your mom or big sister when they got theirs and that may give you some idea of when you’ll get yours.

How will I know if I’ve gotten my period?

Not all periods are red, so you may see some brown or pink fluid in your underwear. Regular vaginal discharge is clear or milky, so if you see something that’s more pink, red, or brown, guess what — you probably just got your period!

All my friends have gotten their period, why haven’t I?

First periods don’t happen at the same time for everyone, and there’s nothing wrong with you if start your period before or after your friends. We asked around in our office and some people got their first periods at 8 years old, others as late as 16 — that’s a big difference! Ask your mom or sister when they got theirs to get a better idea of when your first period will start (yes, first period start dates can be hereditary!).

What does a period feel like?

You may not feel your period flow, instead you’ll just notice some color on your undies. Some people feel a little wetness, more than usual vaginal discharge.

How long does a period last in one month?

The amount of time you’ll bleed every month can vary from 3 to 7 days, but it’s normal for your period to vary a little from cycle to cycle. If you notice blood for longer than 7 days, it’s a good idea to check with your gynecologist to make sure everything is okay.

Will my period hurt?

It shouldn’t. The flow of menstrual fluid out of your vagina shouldn’t hurt at all (you probably won’t even know it’s happening!). Some people get cramps or back aches before they start their period, and those can be uncomfortable, but they shouldn’t be painful. If you are in a lot of pain during your period, set up an appointment with your gynecologist so they can help you feel better — nobody should live with period pain!

Will people know I have my period?

Probably not, unless you tell them. A lot of the signs and symptoms that come with a period are only noticeable to you. But there’s nothing wrong with telling people that you’re on your period, or that you’re feeling a little different because of your period. Sometimes it can make you feel better to talk to family or friends about what’s going on.

Why is my period brown?

Periods come in all different colors and textures — some are more red and liquidy, others may be brown and clumpy. Brown blood is just blood that’s a bit older. Some people notice brown blood before they see red (on or before day 1), others have brown blood at the end of their period (day 5, or whenever your period ends). If you’ve just started your period, you may only see brown stuff, and that’s totally normal. We made a li’l video talking more about this, check it out here.

Sometimes my period is heavy, sometimes it’s light. Why is that?

Periods are different from person to person, and can be different in the same person from cycle to cycle. You may start with a light flow, have heavy days in the middle, and finish off with a light flow; or have heavy flows at the beginning and then lighter days only at the end; or something else! You’ll get to know *your* flow over time and understand what heavy, medium, and light days mean for you.

Can I swim and play sports on my period?

Absolutely! You can do *anything* on your period—swim, dance, wear white pants, go camping, whatever—you may just want to use different period products depending on the activity.

What do you mean when you say “cycle” and “flow”?

When we refer to your period “cycle” we’re talking about the time from when you first start bleeding (day 1 of your period) to when you stop bleeding (could be day 4, 5, 6, or longer). It can also refer to the 21 - 45 day timeframe between day 1 of your last period and day 1 of your new period. When we talk about your “flow,” we’re referring to the fluid that comes out of your vagina (the red/brown/pink stuff).

What is PMS?

PMS stands for Premenstrual Syndrome and it’s often defined by symptoms you may feel, physically and emotionally, before you get your period. PMS symptoms can include cramps, sore boobs, laziness, moodiness, or an appetite for certain foods (we *always* crave pizza!). A lot of times, PMS symptoms show up a few days before your flow starts and can be helpful signs to let you know to wear your Thinx (BTWN) in preparation for what’s to come.

How do I talk to my mom about my period?

It may feel super-awkward, but it doesn’t have to be (hey, your mom has experienced periods, too!). Sometimes it’s easiest just to blurt this kinda stuff out, but you can also write her a note or send her a text if that feels better to you. And, look, it isn’t just moms who can be helpful with first periods: You can always talk to your dad, cool aunt, big sister, favorite teacher, school nurse, or any other adult you trust to give you support and advice. Remember, periods are 100% normal and nothing to be ashamed about! Watch this video for more tips from us on how to talk to your mom about your period.

How do I hide my period from my mom?

You *could* hide it from your mom, but we don’t recommend it. Why? For a few really important reasons: 1. Periods are nothing to be ashamed of or hide. 2. Your mom can probably give you some really awesome tips on what products to use and how to feel better if you have PMS symptoms. 3. Periods can be a great bonding moment, and your mom will probably make you feel really proud of your body and excited to grow up.

Do boys get periods?

Nope, male bodies don’t have the same reproductive parts as female bodies, so they do not get a period. But they have their own unique biological system and go through all their own physical and emotional changes during puberty, too.

Will I have my period forever?

No. Your period will eventually stop when you enter what’s called menopause. This happens for most people between the ages of 45 and 55, and, like your period, menopause will come with some new physical and emotional changes.


What is your mission?

Our mission is to empower every body* through innovative solutions and social change — and we’re doing that with the products we create and the conversations we start.

How does Thinx help underserved communities?

Giving back to people with periods has been at the core of our mission since day 1 — but we know there’s still a lot of work to do (like more education, accessibility, and resources!). That’s why we’re committed to paying it forward through our giveback programs. The best part is that we’re doing it with *your* support! A portion of every Thinx (BTWN) purchase helps fund our giveback initiatives near and far.

Wanna learn more? Email our giveback team at


I love the product, how can I sell Thinx (BTWN) at my store?

Thanks for the support! Our biz is *growing*, and because of the massive interest in our innovative period solutions we're launching a wholesale channel. Interested in selling our stuff? Fill out our contact form to talk more.

Affiliate Programs

Do you have an affiliate program?

Yes. Our affiliate program is managed through Pepperjam. To apply for the program, please sign up here.