We may earn a commission from links on our website, but this doesn't influence the opinions of our editors.

Thinx vs Knix: Which Period Underwear Is Better?

Last Updated: August 16, 2023

Period underwear is steadily becoming more popular these days, but which brand is best? Read our Thinx vs Knix review to see which is the better of the two.

Searching for the best underwear when the red monster comes every month is of utmost importance. Especially when the fear of ruining another perfect pair of panties is plaguing your mind. 

Below, we compare two of the most popular period underwear brands so you can see which one fits your needs. Keep reading to find our thoughts on Thinx vs Knix to help you decide which brand to invest in.  

Plus, for a more in-depth look, read our full Thinx review and Knix review here.

Thinx vs Knix Overview 

Leak-proof, functional underwear has been ignored for many years, but since Thinx and Knix have come onto the scene, leak-proof is the new norm. 

Both brands have a specific eye for leak-proof, versatile, durable period underwear. Since both brands are pretty similar, we’ve broken down their main points below:

– Brand is 100% dedicated to period underwear and garments

– Offers period panties, shorts, and leggings

– Holds 0.5 to 5 tampons worth (depends on underwear)

– Prices range from $20 – $47 per pair

– Offers a large variety of cuts, shapes, and absorbency options

– Has a flow test to help find the best product for you

– Free shipping on your first order, then a $5 shipping fee

– Free returns within 60 days in the U.S. 

– Offers discounted bundle deals and sale section
– Brand also sells regular undergarments and loungewear

– Offers leakproof panties, pads, leggings, shorts, and swimwear

– Holds 1 to 8 tampons worth (depends on underwear)

– Prices for their period panties range from $18 – $42 per pair

– Offers a large variety of cuts, shapes, and absorbency options

– Sizing can be inconsistent

– Free shipping on orders over $75

– Free returns within 30 days

– Offers discounted bundle deals and sale section


Thinx is increasing in popularity as influencers all around the world are preaching about the new age of period undies, so we can get rid of wasteful tampons and pads. Thinx’s goal is to ensure women feel comfortable and confident on their period without having to worry about bleeding through their pads or ruining their clothes. 

Let’s break down this brand into pros and cons to give you a better feel for their company:


  • Offers leakproof, Modal cotton undergarments
  • Includes a wide size range from XXS to 4XL
  • Flow test helps you find the best underwear for your cycle
  • Wide variety of shapes and cuts of undergarments
  • Variety of absorption strength
  • Save money with bundles and the sale section
  • Free returns within 60 days
  • Great customer service


  • Free shipping on first order
  • Import tax on international orders 
  • Only lasts a couple of years
  • Doesn’t offer reusable pads
  • Upfront investment cost, but overall saves money on period products

Best Sellers

Super Hiphugger
Comes in 4 colors
Sizes xs-4x
Comes in 5 colors
Sizes xs-4x


IG: @knix

Knix has improved its brand policies and products drastically over the last couple of years, making it now one of the best undergarment and loungewear brands on the market. They offer seamless and comfortable bras, underwear, leggings, shapewear, maternity pieces, and more (including a wide selection of period underwear). 

We’re going to break this brand into pros and cons to give you a better feel for their company:


  • Offers high-quality undergarments and loungewear
  • Include a wide size range from XS to 4XL
  • Leakproof underwear and reusable pad options
  • Save money with bundles and the sale section
  • Free shipping on orders over $75
  • Free returns within 30 days
  • Responsive customer service


  • Difficulty with sizing charts
  • Only lasts a couple of years
  • Upfront investment cost, but overall saves money on period products

What Customers Are Saying

After searching the web for customers’ thoughts on these brands, we found these top points of feedback:

  • Most of their period panties are great for lighter flow days as a backup to other products like pads and tampons
  • Thinx generally has better absorbency, whereas most customers say Knix is better as a backup only.
  • Customers say Knix is typically more comfortable than Thinx.
  • Knix is also great for other loungewear and undergarments that are comfortable and keep you fresh all day. 
  • Thinx is good for varying cycle flow and comfort throughout the day when on your cycle. 
  • For higher absorbency options, Thinx has a wider variety than Knix


We also wanted to bring to light a recent study involving the use of PFAs (per-and polyfluoroalkyl substances) in some period underwear to help you make the best decision for you.

If you haven’t heard of PFAs before, they are toxic chemicals typically called “forever chemicals” because they never break down, according to the EWG. They are often found in man-made products because of their water and stain-resisting nature.

In 2020, both Thinx and Knix were involved in lawsuits that accused them of using PFAs in their period underwear for moisture-wicking purposes.

An independent study shows that both Thinx and Knix contained “high levels of fluorine,” which is an indicator of the use of PFAs. Since then, Thinx has continued to deny the use of PFAs, stating that all their underwear products “are rigorously tested for harmful chemicals.”

Knix, on the other hand, conducted a third-party study that showed no detection of fluorine in their leakproof underwear.

Obviously, we can’t know the exact truth, but we wanted to give you this information so you can make your own informed decision. 

The Final Verdict

In the end, when it comes to Thinx vs Knix, the brand you should shop for depends on the kind of cycle you have and the coverage you’re looking for.

While Knix does sound a bit better on paper, we’ve had a better experience with Thinx (and so have many other customers). Knix is slightly cheaper, but we recommend investing a few extra dollars into Thinx since the quality is better and they tend to hold more.

Knix states that some pairs can hold up to 8 tampons worth, but many reviewers state that Knix undies don’t hold nearly as much blood as they advertise. On the other hand, Thinx estimates seem to be more realistic.

Those with a very heavy flow might want to proceed with caution and test period undies as a backup. For some, even the highest absorbency options don’t last very long.

Since they both are so similar, remember they both offer free returns, so you can try both brands and figure out which is the right choice for you!

NEXT UP: What Are Period Underwear? Your Ultimate Guide

Leave a Comment