How to choose period underwear: the five decisions, in order

Decision 1: capacity, in millilitres, not in label words

Start here, because it is the decision that fails publicly when it is wrong. Every brand rates its pairs in words - Light, Moderate, Heavy, Super, Overnight - and the words are not comparable. Our claims report shows the same word spanning roughly three times the capacity from one brand to another, so "Heavy" tells you where a pair sits in one brand's range and nothing about how it compares to the next brand.

The fix is to think in millilitres. Describe your flow to the absorbency translator and it returns the tier at each brand that covers it, with each brand's own published claim graded for how well it is evidenced. Pick the tier that covers your heaviest hours with some margin, and treat the label word as a name, not a measurement.

Decision 2: size, from your hip, per brand

Period underwear is sized on a hip measurement, not on the size you usually buy, and the brands disagree with each other. The same hip measurement can be a medium at one brand and a large at the next. Measure around the fullest part of your hips and seat, then let the size finder return your size at every charted brand at once. If you land between sizes, size up for a snug seal at the legs rather than down - a gap at the leg opening is the most common fit-related leak.

Decision 3: the cut

Cut decides comfort and coverage, and it interacts with capacity. Thongs and bikinis carry the smallest absorbent panel and sit at the light end of every brand's range. Briefs, boyshorts and high-waisted styles carry the largest panels and reach further back, which is what you want for sleeping and long sitting, when flow runs toward your tailbone. Most people end up with two cuts: something minimal for light days and something full-coverage for heavy days and nights. The style pages list every brand's pairs in each cut, with capacity on every card.

Decision 4: fabric, and the safety questions behind it

The layer against your skin is either cotton (often organic) or a synthetic wicking fabric. Cotton is more breathable and gentler if synthetics irritate you; synthetics tend to feel drier faster. Underneath, every pair has an absorbent core and a leakproof barrier, so "cotton" always describes the top layer, not the whole pair.

If safety is part of the fabric question for you, the safety hub holds the sourced record: the PFAS settlements, what silver finishes are for, why there is no ingredient list, and what the research says about breathability. None of it requires a chemistry degree, and none of it is marketing.

Decision 5: price, and how many pairs

A pair is more expensive than a box of disposables and cheaper than a year of them. The cost page computes what a year of periods costs from live prices, and the budget guide ranks the cheapest verified pairs. How many you need depends on your cycle length and how often you can wash: a full rotation is usually six to nine pairs, but nobody should buy nine on day one.

Then: buy one pair, not a set

Period underwear is usually final sale for hygiene reasons, and fit, feel and tier are personal. Buy a single pair in the tier and size the tools gave you, wear it through one cycle, and only then expand. If it leaks, the leaking guide walks through the five causes in order. If it is right, the same brand and tier in a second cut is the cheapest possible next purchase, because the size and capacity questions are already settled.