Knix review, and how it compares with Thinx and Modibodi

What Knix is.

Knix started in 2013 with a crowdfunded run of leak proof underwear, and it now sells period underwear, overnight shorts, bladder leak styles, teen lines, swimwear, bras and non absorbent basics. In 2022, Essity, the Swedish company behind several hygiene brands, bought a majority stake. Essity also owns Modibodi. Thinx is majority owned by Kimberly-Clark. So the three best known period underwear brands now sit inside two of the largest companies in feminine care, which explains the wide retail reach and the steady stream of new styles.

We did not wear Knix for this review. We read what Knix, Thinx and Modibodi publish about absorbency, sizing, care and testing, and the Amazon listings for each product we link. Our method is on how we review.

The absorbency ladder.

Knix rates every leak proof piece on one scale, which is the most useful thing about the brand:

Knix level	Absorbs (per Knix)	Use it for
Essential	No absorbency	Everyday underwear
Light	1 to 3 regular tampons	Spotting, discharge, cup or disc backup
Moderate	2 to 4 super tampons	Start and end of a period
Heavy	4 to 7 super tampons	A full day on moderate flow
Ultra	7 to 11 super tampons	Heaviest days, overnight, postpartum

The Super Leakproof styles, including the High Rise, Boyshort and Dream Short, sit at Heavy. Like every brand, Knix uses its own test to translate what a gusset holds into tampons, so the numbers are best used to compare Knix pieces with each other.

Which Knix to buy.

Super Leakproof High Rise. The one to start with. Heavy absorbency with more coverage than a bikini, so it suits most days of a period on its own. Knix High Rise on Amazon.

Leakproof Boyshort. Heavy absorbency, 4 to 7 super tampons per the listing, with more coverage at the sides. Good if you leak at the leg or prefer a short cut.

Super Leakproof Dream Short. A sleep short that covers front to back, where overnight leaks usually happen. Warm in summer, reassuring on a heavy night.

Leakproof Swim Shorts. Knix's swim line rates the shorts at Moderate, 2 to 4 super tampons per the listing, with UPF 50+ fabric. On heavy days, wear them over a disc or cup. More in the best period swimwear.

PFAS and testing.

PFAS are long lasting chemicals once used for water and stain resistance, and the EPA describes them as persistent in the environment and the body. Period underwear has faced PFAS scrutiny, and both Knix and Thinx have settled US class actions over earlier PFAS related marketing claims.

Knix now says it has run routine third party testing for PFAS and organic fluorine since January 2020, that results have been non detect at its labs' limits, and that it does not intentionally use PFAS. Its testing page names the limits it tests to and the supplier controls it uses. Thinx states its products are not made or treated with PFAS. If this matters to you, read each brand's current testing page rather than relying on a "non toxic" label.

Fit, feel and care.

Knix pieces are thin for their absorbency, which is the main reason people stick with the brand. Size by the Knix chart, not your usual size: the seal at the leg is what prevents side leaks, so a slightly snug fit is better than a loose one.

Care is the same as any period underwear. Rinse in cold water until it runs clear, wash cold, skip fabric softener and bleach, and line dry. Tumble drying and softener are the fastest ways to wear out the absorbent and barrier layers. A pair that starts to leak at its usual load has reached the end of its life.

Knix vs Thinx vs Modibodi.

	Knix	Thinx	Modibodi
Owner	Essity (majority)	Kimberly-Clark (majority)	Essity
Absorbency scale	Five levels, in tampons	Up to 12 regular tampons (period line)	Light 4, Moderate 6, Super 10 tampons (Australian site)
Sizes	XS to 4XL	Wide range	Wide range
PFAS position	Tests since 2020, non detect	Not made or treated with PFAS	Check the brand's current page
Lower cost line	No	Thinx for All	No
Swim line on Amazon US	Yes	Check the brand	Not on Amazon US
On Amazon US	Yes	Yes	No

Choose Knix if you want the clearest absorbency ladder, the widest sizing and a full swim and sleep range.

Choose Thinx if you want the brand with the highest headline capacity claim, or a lower cost two pack from Thinx for All. Our pick is the Thinx Breathable Hip Hugger.

Choose Modibodi if you prefer to buy direct and like its fabrics and cuts. It covers period, swim, sleep, active and teen ranges, with a 3 layer gusset per the brand.

Who Knix suits.

• Anyone moving away from pads who wants one brand for light, heavy and overnight days.
• People who use a menstrual cup or disc and want reliable backup.
• Postpartum bleeding, when internal products are off limits until you are cleared; Ultra and Dream Short styles are the ones to look at. Our postpartum dryness guide covers what else changes after birth.
• Light bladder leaks, which Knix covers with a separate line.

Who might skip it.

If you have very heavy periods, no period underwear is likely to work alone all day; pair it with an internal product, and see a clinician if you need to change every 1 to 2 hours. If you react to synthetic fabrics, try a cotton or modal style first. And if lowest cost per pair is the priority, the multipacks in the best period underwear go further.

The verdict.

Knix is the period underwear brand we would buy first, for its clear absorbency levels, broad sizing and published testing. Start with one Super Leakproof High Rise, add a Dream Short if you leak overnight, and keep a light pair for backup with a cup or disc. Thinx is a close second and a fine choice if its cut fits you better. None of this is medical advice.