Frequently asked questions

Flissie boxers are 95% Tanboocel bamboo viscose and 5% elastane. Tanboocel is a closed-loop bamboo viscose where the chemicals used to process the fibre are recovered and reused rather than released, making it one of the more sustainable forms of bamboo fabric available. The result is a knicker that feels closer to silk than cotton — soft, breathable, naturally temperature-regulating, and gentle on sensitive skin.

For most use cases, yes. Bamboo viscose wicks moisture roughly 40% better than cotton, dries faster, and stays cooler in heat and warmer in cold thanks to its natural micro-gaps. It's also significantly softer and less likely to irritate sensitive skin. Cotton still wins on durability over many wash cycles, but for comfort, breathability and anti-chafing, bamboo is a clear step up.

The 6" is a shorter style that sits roughly mid-thigh — great under skirts, dresses, gym shorts, or for anyone who finds longer leg lengths too warm. The 9" extends to about an inch above the knee, fully covering the inner thigh — the right choice if your priority is anti-chafing on long walks, runs, festivals, hot weather, or under flowing dresses where you don't want any thigh-rubbing.

Flissie are designed specifically for the female form. The waistband, cut, and rise are all engineered around women's anatomy — they sit comfortably over the hip without digging, and the gusset is shaped for women. They're called "boxers" because the silhouette is boxer-style (longer leg, looser fit than briefs), not because they're borrowed from menswear.

When you're between sizes, size up. Flissie boxers are designed to fit close to the skin without compressing — going down a size compromises the anti-chafing function because the fabric needs full contact with the thigh to glide rather than friction-bunch. Most between-size customers report the larger size feels exactly right after one wear; the smaller size never quite stops feeling tight.

Yes — we carry every size from UK 8 to UK 30 in the same colours and inseam options. The 9" inseam in particular has become a staple for women in sizes 16+ who have struggled for years to find anti-chafing underwear that actually fits properly without rolling, digging or rising up. The full size guide is on our size guide page.

No — and this is the single most common review comment from women who've tried other brands first. Flissie boxers are cut with a specific leg-band tension and bamboo viscose's natural cling against skin to stay in place through walking, running, and dressing changes. If you've had Boody, Step One, or M&S boxers roll up before, this is the design difference you'll feel immediately.

Flissie boxers are designed without a hem ridge, so there's no VPL (visible panty line) under leggings, fitted dresses, or slim trousers. The boyleg cut means there's no waistband indent either. For the smoothest finish under very fitted fabrics, the 6" inseam in a nude shade is the most invisible combination; the 9" is best under skirts and dresses where the leg length isn't an issue.

Yes — bamboo viscose's moisture-wicking and temperature-regulating properties make Flissie boxers one of the most-recommended options in our review base for perimenopausal and menopausal women. The fabric pulls heat and sweat away from the skin in night sweats and day-time flushes, and the breathable knit doesn't trap moisture. Many customers buy the 9" inseam to sleep in and the 6" for daytime.

Many of our customers find Flissie boxers more comfortable than traditional postpartum pants in the weeks after birth — the soft, non-digging waistband sits above or below a C-section scar without rubbing, the gusset is wide and gentle, and the longer leg lengths prevent chafing during a recovery period when movement might be limited. They're not designed as surgical garments — for those, consult your midwife or GP.

Yes — this is what Flissie was originally designed for. The 9" inseam in particular extends past the point where thighs typically rub, and the bamboo viscose creates a smooth, low-friction surface that lets your thighs slide against each other rather than catching. Customers regularly report doing Camino walks, half-marathons, and festivals chafe-free for the first time in years.

Bamboo viscose is naturally hypoallergenic and antimicrobial, and Flissie boxers are dyed using OEKO-TEX Standard 100 certified processes (no harmful chemicals). Customers with eczema, allergic dermatitis, lichen sclerosus and post-radiotherapy sensitivity routinely report Flissie as the only underwear they can wear without flare-ups. If you have a specific skin condition, we recommend trialling a single pair first.

You can wear Flissie boxers comfortably on light days or as a backup layer with a pad or period pants underneath. They aren't designed as leak-proof period underwear themselves — bamboo viscose absorbs but doesn't trap fluid the way a multi-layer period gusset does. For heavy days, pair them with period-specific products; for the rest of your cycle, they're often more comfortable than standard knickers.

Machine wash at 30°C with similar colours, inside out if you want to preserve the dye. Use a gentle detergent — skip fabric softener (it coats bamboo fibres and reduces breathability). Air dry where possible; tumble drying on low is fine but shortens fabric lifespan. Avoid bleach. With proper care, a pair typically lasts 18–24 months of regular wear before noticeable wear.

Like all dyed fabrics, deep colours (Black, Pine Forest, Plum Pink) will fade slightly over many wash cycles — washing inside out, in cold water, and air drying preserves the colour significantly longer. Our Lavender, Nude and lighter colours are dyed using a process designed for minimal fade. If you notice colour transfer in early washes, wash separately for the first 2–3 cycles.

The most-worn pairs in our review base report 18–30 months of regular rotation before any visible wear. Bamboo viscose isn't as durable as heavyweight cotton over very long timelines, but it dramatically outlasts most fashion underwear and synthetic blends. The first thing to wear is usually the elastic in the waistband — when that goes, it's time to replace the pair.

Tanboocel is a closed-loop bamboo viscose, meaning the solvents used to break the bamboo down into fibre are captured and reused rather than released as waste. It uses roughly 97% less water than cotton production and bamboo plants regrow without replanting, fertiliser, or pesticides. It's not zero-impact — no fabric is — but it's meaningfully better than conventional cotton, polyester, or older viscose processes.

For every three pairs of Flissie boxers sold, we donate one pair to a woman facing period poverty, homelessness, or domestic abuse through our charity partners. Comfortable, clean underwear is consistently named as one of the most-requested but rarely-donated items in women's shelters. The programme is built into the cost of every pair we sell — you don't pay extra.

Flissie boxers are designed in the UK and manufactured by our partner factory which holds OEKO-TEX Standard 100 certification and meets ethical labour standards. We visit our manufacturing partners regularly. We're working toward full B-Corp certification, and our long-term goal is to bring more of the manufacturing chain closer to the UK as volumes allow.

We offer a 60 day return window on unworn pairs in their original packaging — and a separate "fit check" guarantee on your first order, where you can try one pair on and still return the rest unopened. Returns are at your cost. Details and the returns email are on our returns page.