The Science

What the research actually says about underwear.

Every claim sourced. Every uncomfortable finding included. No medical advice — just the textile science and the peer-reviewed papers.

1. The moisture story — measured, not vibes

Almost every underwear brand says something about "breathability." Almost none of them put a number on it. The numbers exist; here they are.

How much water each fibre actually holds

The textile-science measure is moisture regain — the percentage of a fibre's dry weight it absorbs at equilibrium at 20°C and 65% relative humidity. It's defined by ASTM standard D1909, and the values for the four fibres relevant to underwear are well-established¹:

Cotton soaks up about twenty times more water than polyester and roughly twice as much as nylon. That's why a sweated cotton gusset stays damp against the skin while a nylon shell sheds the moisture and moves on.

How long it takes to dry

The same difference shows up in drying-time studies. Under standard AATCC 199 test conditions (37°C, gravimetric), a polyester fabric reaches 95% dry in 2–3 hours; an equivalent cotton fabric takes 8–10 hours². A 2025 peer-reviewed study in Materials independently ranked polyester fastest and cotton slowest across four separate drying protocols³.

Translated: a sweated cotton gusset can still be damp four hours after a Pilates class. A nylon body dries before you've finished showering.

How fast moisture moves through the fabric

The other relevant measurement is moisture vapour transmission rate (MVTR) — how quickly water vapour passes through the fabric, tested by ASTM E96⁴. Synthetic knits consistently move vapour faster than equivalent cotton knits because the fibre itself doesn't grab the water — the knit structure and the fibre's surface chemistry let it through⁵. (Honest caveat: MVTR varies 5–10× with knit gauge, finish, and test method, so it's worth knowing the numbers are real even when the headline is hard to summarise in a stat.)

Why activewear has been performance nylon since the 1970s

The textile-engineering case is four measured properties of nylon 6,6: tenacity of 33–44 cN/dtex (highest of common apparel fibres), abrasion resistance above 50,000 Martindale cycles (cotton typically fails at 10,000–20,000), low moisture regain, and elastic recovery that lets it stretch and return without bagging⁶. It's why your swimsuit, your activewear, and your hosiery have all been polyamide for decades. We just put it under your leggings too.

2. Why the gusset is cotton (and why that's the most evidence-based part of underwear design)

Most women have been told, more or less since high school, that cotton underwear is "healthier." It is worth knowing how much real research is behind that. The honest answer: less than you'd think — but the bit that is well-supported is the gusset, which is exactly where we put the cotton.

What the literature actually shows

There is no well-powered randomised trial showing that cotton underwear reduces bacterial vaginosis, yeast infection, or vulvar irritation in healthy (non-symptomatic) women. The largest modern study on the subject — the B-THONG survey, Hamlin et al. 2019, n=986 — found no significant difference in UTI, BV or yeast rates between thong and non-thong wearers. The only fabric signal that surfaced was that a non-cotton gusset was associated with yeast vaginitis⁷. Body fabric: no signal. Gusset fabric: signal. Tells you where the action is.

Going further: Runeman et al. 2005 (Acta Dermato-Venereologica) put thirty-two healthy women through a crossover study to test whether tight-fitting "string" underwear changed vulvar skin temperature, humidity, pH, or aerobic microflora compared to regular underwear. The finding was negligible differences across all four measurements⁸. The headline assumption that synthetic underwear traps moisture against the vulva in a way that meaningfully alters the local environment did not survive direct measurement, at least in healthy women.

What the gynaecology bodies actually say

The cotton recommendation does exist in patient-information literature from ACOG (American College of Obstetricians and Gynecologists) and the RCOG (Royal College of Obstetricians and Gynaecologists, UK) — but in both cases the recommendation is aimed at women experiencing vulvar irritation, pain or recurrent infection, not as general guidance for asymptomatic women. The RCOG patient leaflet on vulvar skin conditions advises "loose-fitting cotton or silk underwear (rather than synthetic, dyed underwear)" — for women with vulvar skin conditions⁹. ACOG's persistent-vulvar-pain guidance recommends 100% cotton; again, for symptomatic women¹⁰. These are expert-opinion recommendations, not trial-graded evidence.

Where the consistent signal points — and where our cotton sits

Synthesising the literature: the orthodoxy that "cotton underwear is healthier than synthetic" is weaker than the messaging implies, but the consistent signal across the studies and the guideline language is that the gusset is where the fabric choice matters. The vulva contacts the gusset; the rest of the underwear contacts skin that is no more sensitive than skin anywhere else on the body.

Our Gym G is performance recycled nylon for the body — which solves the moisture-retention, drying-time and visible-panty-line problems cotton cannot — and cotton-lined in the gusset, which puts cotton in the only place every line of evidence converges on. That's not a compromise. It's a design that takes both the textile science and the vulvar health literature seriously.

3. The odour story — be honest about who's actually responsible

Body odour is one of the most-misunderstood pieces of fabric science. The fabric isn't producing the smell. Bacteria on your skin are. The fabric just affects the conditions they're working in.

Sweat itself is essentially odourless

Eccrine sweat — the kind your glutes, groin and skin generally produce in response to heat or exercise — is about 99% water, plus sodium, chloride, small amounts of potassium, lactate, urea and amino acids¹¹. On secretion, it doesn't smell. The odour shows up when skin bacteria metabolise the sweat (and skin lipids) into volatile compounds.

The bacteria-to-odour mechanism

The most-studied odour molecule in body odour research is 3-methyl-3-sulfanylhexan-1-ol (3M3SH) — the "rotten onion" note. It's produced when Staphylococcus hominis cleaves an odourless precursor (S-Cys-Gly-3M3SH) using a specific enzyme, releasing the volatile thioalcohol¹². That's the mechanism. The fabric is the substrate, not the source.

The honest comparison — cotton vs synthetic on odour

What is defensible: the gusset — the area that produces the most odour-relevant moisture and where bacterial activity matters most — is cotton-lined. The synthetic body sits where the sweat-and-bacteria load is much lower (your hips, your glutes — these aren't the bits producing the odour profile). Fast drying of the nylon body further reduces wear-day moisture retention. The full picture is: cotton where the science says you want cotton; performance nylon where the science says you want performance nylon.

4. The cognitive cost of underwear you can feel

Our brand line is "underwear you forget you're wearing." That isn't a vibe. There's a measurable cost to not forgetting — and the cost is bigger than most people realise.

Why steady underwear becomes invisible — and shifting underwear doesn't

When skin receives a steady, predictable touch input (a well-fitted waistband sitting still), your somatosensory cortex adapts. Chen et al. measured it directly: cortical activity in the primary and secondary somatosensory cortex drops exponentially under sustained fingertip pressure¹⁴. Your brain literally stops listening. That's the mechanism of "I forgot I was wearing it."

The opposite mechanism is the load-bearing finding of this whole page. In a 2014 study published in PAIN, Jepma and colleagues ran 100 participants through 24 thermal stimuli across eight forearm sites. When the stimulus stayed in one place, participants habituated — the sensation faded. When the stimulus migrated between sites — i.e., it shifted — they sensitised. The sensation got more noticeable as the day went on, not less. The model explained 93% of variance, and 74 of 100 participants sensitised to the migrating stimulus¹⁵.

A waistband that digs as you walk, a thong that rides up over the morning, a leg-elastic that prints and releases each time you sit — these are migrating stimuli. The neuroscience says they will sensitise. They will get more annoying through the day, not less. This is why "comfortable enough to forget about after a while" doesn't actually happen with the wrong cut of underwear — it gets worse instead.

What that costs you, in numbers

The cost of not-forgetting is documented across several fields. Each row below is a measured cost, with a citation.

Read together: a thong that doesn't move, a band that doesn't dig and a leg-line that doesn't print isn't a comfort luxury. It's the difference between underwear your nervous system stops processing within minutes and underwear that sensitises and steals attention all day.

The implication for sensory-sensitive wearers

For women with sensory processing sensitivity (about 15–20% of the population²⁰) and for autistic or ADHD adults, the habituation pathway is less reliable in the first place. Clothing tactile sensitivity is widespread — in the MacLennan 2023 study of autistic adults, 73% regularly avoid certain clothing, 56% cut labels off, 49% avoid constricting clothes, 47% avoid clothing with seams against skin, and the researchers documented clothing tactile sensitivity as a barrier to gaining and maintaining employment²⁰. This isn't a niche concern. Quiet underwear — no seams against the skin, no shifting pressure, no migrating stimuli — is a baseline accessibility design, not a premium feature.

5. So this is the design

You can read the four sections above as four separate stories. They're actually one story.

Cotton holds water. Synthetic doesn't. So the body of the underwear is performance recycled nylon — fast-drying, no VPL, no leg-line — and the gusset is cotton, because the vulvar-health literature consistently points to the gusset and only the gusset. Bacteria, not fabric, produce odour, and they work faster on retained moisture — so the fast-drying nylon body keeps the wear-day moisture window short, and the cotton gusset handles the area where moisture-and-bacteria matters most. And the only reason any of this matters is that your brain sensitises to shifting pressure across the day — so a thong with no back seam, no leg-elastic, and a flat waistband isn't selling you on a feeling; it's removing the things your nervous system would otherwise spend the day monitoring.

One product. Four design decisions. All four backed by research that exists, that we can point you at, and that we've cited below.