The State of Period Underwear Claims, 2026

Key findings

1. Across the 13 brands tracked, 39 current absorbency-tier claims are published. Only 8 of them (21%) state a millilitre figure directly (grade A). 25 are tampon counts we converted at the brand's own stated or the standard basis (grade B), and 6 rest on conflicting or unconfirmed sources (grade C).
2. The word “Heavy” spans 20 to 63 mL across brands - a 3.1x spread behind one word. A shopper buying “Heavy” has no way to know which end she is getting.
3. “Light” is worse: 5 to 20 mL, a 4x spread. Modibodi's “Light” (20 mL) claims as much capacity as Saalt's, Proof's, and WUKA's “Heavy” (20 mL each).
4. The identical phrase “12 regular tampons' worth” means 60 mL at WUKA, which states 5 mL per tampon and states the 60 mL, and 72 to 108 mL at Thinx, which states no millilitre figure for its period underwear at all. The spread is the FDA's own regular-tampon range of 6 to 9 grams (21 CFR 801.430). Identical words, up to 80% more capacity.
5. The highest brand-stated figure is Knix Ultra, at up to 99 mL (grade C: the brand's own pages state different tampon counts, so the range is shown). The highest figure in the table, about 108 mL for Thinx, is our computation, not the brand's: Thinx gives one claim for its whole current line (All Day, All Night and Teens carry the same “up to 12 regular tampons' worth”), with no per-tier ladder and no millilitre figure, and we carry it at the FDA regular-tampon ceiling, marked computed wherever it appears.
6. 4 of the 12 brands with a current ladder top out at or below 25 mL - below where Knix's “Heavy” tier begins (36 mL). The category's ceilings differ far more than its tier words suggest.
7. At live prices, the cheapest claimed millilitre in stock is Thinx's Active Mesh Bikini at $19 for an up-to-108 mL claim - $0.18 per claimed mL. Brand medians span roughly 13x between the cheapest and the most expensive claimed millilitre.
8. The only published study using blood components (BMJ Sexual & Reproductive Health, 2023) poured blood slowly onto three pairs of one unnamed brand's super-absorbency underwear until it pooled: under 3 mL each, 2 mL on average. That is one product under one method, a different measurement from a saline-test maximum, not a ranking of the claims here. Every number in this report compares brands like for like; none of them is a leak-free guarantee.
9. Since the 2026 verification pass: Ruby Love removed capacity claims from its product pages entirely, Thinx's classic four-tier ladder disappeared from current marketing, Proof's direct store ended fulfillment (the brand continues at retail as “Proof. by Always”), and Cora exited period underwear altogether. Details in “What changed” below.

What changed in 2026

Recorded during the June 2026 verification pass against each brand's own pages, and tracked weekly since:

• Ruby Love pulled its capacity claims. Product pages that previously stated a 2.5-tampon capacity now publish no capacity claim at all (“can be worn alone or with a pad, tampon, or menstrual cup depending on your flow”). Our catalog shows those products unlabeled rather than inheriting the old figure.
• Thinx retired its classic ladder. The per-tier Light/Moderate/Heavy/Super figures no longer appear in current product marketing; in their place, one blanket claim - “up to 12 regular tampons' worth”, with no millilitre figure - is printed across All Day, All Night, and Teens styles alike. 2026-09-05: Thinx's 100 mL figure re-read as the bladder-leak line's; the period line carries a computed 108 mL from its 12-regular-tampon claim.
• Proof's direct store wound down. shopproof.com stated it would fulfill orders only until 2026-01-30; the brand continues at retail as “Proof. by Always” (P&G), where tier names overlap confusingly with the old direct line - the retail “Super Heavy” brief matches the old overnight tier's 7-tampon claim, not the old “Super-Heavy” tier's 5.
• Cora exited period underwear. Its period-underwear page 404s and the category is gone from its navigation.

Method, limits, and reuse

Every figure is the brand's own published claim, normalized to millilitres at the brand's own stated basis where one exists (1 regular tampon is treated as about 5 mL otherwise, the common industry figure), and graded: A when the brand publishes millilitres directly, B when we converted its tampon counts, C when its own sources conflict or the claim is not first-party confirmed. The methodology has the conversion rules, per-brand sources, and the corrections policy - brands are invited to submit corrections, which we publish.

This report and the dataset behind it are published under CC BY 4.0: quote it, chart it, or republish it with attribution and a link. The machine-readable form is the JSON feed.

Cite as: PeriodFinder, “The State of Period Underwear Claims 2026,” published 2026-07-29. Claims verified 2026-06-05 to 2026-06-11; prices from the live catalog, checked 2026-10-04.