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Home / Shop All / Leakproof UltraThin Boybrief
Exclusive Reward

Leakproof UltraThin Boybrief

$34.00 USD

Absorbs about 2.5 super tampons

Invisible under clothes

Moderate protection without the bulk

Machine washable

| Warm Sand
| Warm Sand
| Warm Sand
| Warm Sand

Absorbency: Moderate

Moderate
about 2-4 super tampons
Ultra
about 7-11 super tampons

Color: Warm Sand

Size:

True to Size

•

Size:

Size and Fit Guide

Free Shipping on orders $100+

Shipping

Shipping

Processing Timelines

Please allow 1-2 business days for our warehouse team to pack and ship your order. During peak periods such as sales, holidays and product launches, please allow up to 4 business days for us to process your order. Once an order is placed, we cannot guarantee any address updates, order changes or cancellations. Orders placed on Friday after 1PM will not be shipped until the following Monday.


Split Shipments

Most orders will ship from a single warehouse. However, we occasionally ship from a combination of warehouse locations, so you may receive your order in multiple parts. If items from your order ship in separate packages, we’ll send you tracking information for each package when it becomes available.

Delivery Timelines

For the most up-to-date delivery time estimates, please refer to the shipping timeline at checkout. Delivery timelines do not include processing times. See above for details. All transit times are measured in business days which are Monday-Friday, excluding holidays.

Please note, all shipping timelines are estimates and are not guaranteed.

We are not able to ship to US territories (including Puerto Rico, U.S. Virgin Islands, Guam, Northern Mariana Islands and American Samoa) at this time.
Easy Exchanges within 30 Days

Returns

Returns

Sale & Last Call

Items discounted 30% and below are eligible for size exchange or store credit. Items discounted above 30% and above are final sale – no refunds, store credits, or exchanges can be accommodated.

Free Returns

Knix covers the return shipping fees for exchanges and refunds initiated through our Return & Exchange Portal. Exchange orders initiated through our Return & Exchange portal are also eligible for free shipping within the USA and Canada. Please note, the shipping fees on your original order are non-refundable.

Return Policy

Return policy varies by product, please check if your item is refund or exchange eligible by viewing our full policy here.
Rewards Members Earn 34 Points

Comfort-First Fit

Mid-rise boybrief silhouette with full bum coverage for a smooth, comfortable fit.

Worry-Free Protection

Our newest leakproof innovation provides more absorbency without the bulk. Patented 360 LeakSeal™ technology locks in leaks at every edge.

Moderate Absorbency

Absorbs 2.5 super tampons worth of liquid—perfect for moderate flow days, light bladder leaks, and sweat. The carbon cotton gusset top layer keeps you dry.

No-Show Style

Buttery-soft and smooth fabric gives a seamless look and feel. Disappears under clothes, even leggings.

Easy to Wash

Machine washable just like regular underwear.

Zoom

| Warm Sand
| Warm Sand
| Warm Sand
| Warm Sand

How to Choose?

Essential

  • • Days you don’t need leak protection. Everyday freshness and moisture wicking.
  • tsp
    0 tsp

Heavy

  • • Extra peace of mind. For the first days of your cycle, light bladder leaks, or a full night's sleep without a leak.
  • tsp
    about 8-14 tsp
  • pad
    about 1.5-3 regular pads
  • tampon
    about 4-7 super tampons
  • cup
    about 1.5-3 menstrual cups

Light

  • • Daily freshness. For sweat, discharge, period spotting, or backup protection.
  • tsp
    about 1-3 tsp
  • pad
    about 1-3 pantyliners
  • tampon
    about 1-3 regular tampons
  • cup
    about 0.5 menstrual cups

Moderate

  • • For mid-cycle flow, surprise cough or sneeze leaks, or a really sweaty spin class.
  • tsp
    about 4-8 tsp
  • pad
    about 1-1.5 regular pads
  • tampon
    about 2-4 super tampons
  • cup
    about 0.5-3 menstrual cups

Ultra

  • • Ultimate peace of mind. For the heaviest period days, light bladder leaks, unexpected postpartum flow, or overnight protection.
  • tsp
    about 15-20 tsp
  • pad
    about 1.5-2.5 super pads
  • tampon
    about 7-11 super tampons
  • cup
    about 2-3 menstrual cups

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4.6
Rated 4.6 out of 5 stars
Based on 14 reviews
Total 5 star reviews: 12 Total 4 star reviews: 0 Total 3 star reviews: 1 Total 2 star reviews: 0 Total 1 star reviews: 1
86%would recommend this product
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14 reviews
  • Rated 5 out of 5 stars
    21 seconds ago
    Must buy

    Great fit! Great color! Work well

    Robyn J.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 week ago
    Couldn’t Ask for a Better Fit

    These are the best fitting underwear and leakproof to boot

    Sherrie B.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 week ago
    Seamless

    I love that these are seamless! Can’t tell with leggings on! Super comfortable !

    Jeannie C.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 week ago
    Very comfortable period underwear

    Love this brand despite the cost.

    Marlyn G.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 week ago
    Boybrief

    Bought for first time. Love the fit and comfort. On

    Lynn M.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    2 weeks ago
    Love these

    I have been a big fan of the boyshort knix so decided to try these and I swear they are even better! I will be getting more and would like knix to make more boyshort/boybrief underwear as I love the fit

    Laura S.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    3 weeks ago
    5 Stars

    Have loved these undies for years! They fit totally comfortably and do the job for sneezes and such, and i mean they so the iob! Somehow the ones i ordered recently are even lighter and more comfortable! Very worth the money and they really last, especially when allowed to air dry.

    Dawn
    Was this helpful?
  • Rated 5 out of 5 stars
    1 month ago
    Leakproof Ultra Thin

    These undies feel so sleek against my skin- love that feel.

    Aline H.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 month ago
    Boybrief

    Great , highly recommend

    Susan K.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    1 month ago
    Great fit

    I love the fit and comfort of these panties.

    Dianne E.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    2 months ago
    Sits just right

    Not too low, not to high!

    Amélie L.
    Verified Buyer
    Was this helpful?
  • Rated 5 out of 5 stars
    2 months ago
    Boybrief

    Love these. Super comfy and do the trick!

    Bronwen W.
    Verified Buyer
    Was this helpful?