How Thinx and Aisle period underwear compare on the only thing that travels across brands - capacity in millilitres - plus how each one's sizing runs. No brand's thumb on the scale.
Verified against the brands' own pages 2026-09-05 · Every capacity is the brand's own claim, graded and dated
By their own published claims, Thinx reaches a higher maximum capacity (up to 108 mL) than Aisle (up to 40 mL) at its highest current tier. That does not make every Thinx pair more absorbent than every Aisle pair - it means the top of Thinx's range is higher. Compare tier by tier in millilitres, not by the label words.
Not quite like for like: Thinx converts from a tampon count (grade B), Aisle states its figures in millilitres (grade A). Cheapest in-stock pair today: Thinx $19, Aisle $27.20.
Every capacity above is the brand's own maximum claim, typically from a saline saturation test. The only published study with real 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 a different measurement, not a ranking of these claims. Use the numbers to compare the two brands like for like, not as a leak-free guarantee.
In stock now, from each brand
The pairs behind the ladders above, with today's price and a buy link. Every card also opens our graded data page for that pair.
The 3 in-stock pairs from each brand with the highest verified capacity claim, from the live catalog, highest first. Where a brand publishes no per-product capacity we can verify (Ruby Love pulled its claims), its 3 cheapest in-stock pairs instead, and the cards say so by showing no millilitre figure. Prices and stock are from the weekly refresh; a brand with nothing in stock shows no cards.
Sizing
Thinx is presented as true to size by the brand; Aisle is one many people size up in. Both brands size from your hip measurement, so rather than converting one brand's size into the other's, the size finder gives you your size in each directly.
Thinx: Thinx says its styles are completely true to size and to follow your hip measurement, measured at the widest point. By design they fit a little more snugly than regular underwear for leak protection, not undersized. The Teens line fits true to size and is narrower at the thigh.
Aisle: Aisle says to size up if you are between sizes on briefs and hipsters, and that the 1X is roomier through the waist than the XL. Its thongs run large in 1X and 2X, so Aisle recommends sizing down for those. Aisle sizes off the widest part of the lower hip and publishes no waist measurement.
Quick answers
Is Thinx or Aisle more absorbent?
By their own published claims, Thinx reaches a higher maximum capacity (up to 108 mL) than Aisle (up to 40 mL) at its highest current tier. That does not make every Thinx pair more absorbent than every Aisle pair - it means the top of Thinx's range is higher. Compare tier by tier in millilitres, not by the label words. These are saline-lab maximums, not leak-free guarantees; the one test with real blood (BMJ 2023, three pairs of one brand) measured a few millilitres before pooling, a different measurement from a claimed maximum.
Do Thinx and Aisle use the same absorbency labels?
No. Thinx gives one figure for all its current styles (about 108 mL) and Aisle publishes 4 current tiers (5–40 mL across the range). Even where the words overlap, the millilitres differ, which is exactly why this page compares them in millilitres with a data-quality grade on every number.
How do Thinx and Aisle sizes compare?
Thinx is presented as true to size by the brand; Aisle is one many people size up in. Both size from your hip measurement, so the size finder gives your size in each brand directly rather than guessing from the other brand's number.
Is Thinx or Aisle better?
Neither is better across the board - they differ on measurable things. Compare three numbers on this page: the millilitres at the tier you actually need (not the tier names), how each brand's sizing runs for your hip measurement, and current prices in the catalog. The right brand is the one whose numbers fit your flow and your body, and that answer differs by person.
Skip the comparison - get your answer
Tell the translator your flow and it gives the covering tier at both Thinx and Aisle. Tell the size finder your hip and it gives your size in each.
