We make women's bamboo boxer shorts, so we have an interest here. We have tried to be useful about what works at the gym rather than just selling you ours. Competitor specifications checked against their own sites in August 2026.
The short version
For most gym sessions, a longer leg in a breathable fabric beats a brief. It stops thighs rubbing, it does not cut across your hip under a waistband, and it will not ride into a wedgie the moment you squat.
Three things decide whether it works:
- Leg length. Under 6 inches and it will not reach where thighs touch
- The right size. These work through skin contact, so sizing up beats sizing down
- Fabric. Anything that holds damp against you is worse than anything that moves it
The options, compared
The brands people actually weigh up for the gym, with the specifications each publishes. We are one of them, so read the last column accordingly.
| Fabric | Longest leg | Best for | If you have worn them | |
|---|---|---|---|---|
| Runderwear | 92% recycled polyamide, 8% elastane | 8 inch long boxer | Hard cardio and running | No returns once worn |
| Flissie | 95% bamboo viscose, 5% elastane | 9 inch | Classes, weights, walking, hot rooms | 60 days, free swap on your whole first order |
| Boody | Bamboo viscose, seamfree | Boyleg, short | Low-sweat sessions, no visible line | 30 day comfort guarantee |
| Step One | Viscose derived from bamboo | Not published | Everyday, budget | 30 day first pair guarantee |
| Sports brands | Polyester and nylon blends | Varies widely | High-output training | Varies |
Runderwear is the specialist and it shows. 360 degree seamless construction, flatlock edging, silicone grippers around the leg hems to stop them travelling, and a recycled polyamide that dries faster than anything natural. If you run or do hard cardio, they are the technically better product. Two things to weigh: they are more expensive than most, and they do not accept returns on underwear once it has been worn.
Boody is genuinely seamfree, which we are not, so under very fitted leggings they will show less. Their range is far wider than ours and goes to 4XL. The limitation for the gym is leg length: their boyleg is short, so it will not reach where thighs touch.
Step One is the cheapest bamboo option, at £15 with many colours discounted to £9 when we checked. They do not publish an inseam for the women's Body Short, which matters if you are buying to stop thighs rubbing.
And us. A published 9 inch leg, the longest in this table, in a fabric that breathes rather than traps heat. We are not the fastest-drying option and we are not seamfree. For classes, weights, walking and hot rooms we would back ours. For a hard summer run, buy the Runderwear.
What goes wrong with normal underwear at the gym
It rides up. A brief with a high leg cut has almost nothing holding it in place once you start moving. Squats, lunges and anything on a mat make it worse.
Thighs rub. No coverage means skin on skin, and by the second half of a class that stings.
The waistband sits exactly where your leggings' waistband sits. Two elastics in the same place is a mark on your skin and a line under your clothes.
It stays damp. Cotton absorbs sweat and holds it. That is fine for a walk and unpleasant for an hour of cardio.
What to look for
A leg of 6 inches or more. This is the whole point. Most underwear marketed to women stops between 2 and 4 inches, which does not reach where thighs actually touch.
A wide, flat waistband. It should sit above or below your leggings' band, not on it.
Flat, bonded or seamfree edges. Overlocked seams sit proud and rub under a fitted legging.
A fabric that moves moisture rather than absorbing it. Bamboo viscose, modal and technical synthetics all do this. Cotton does not.
Check the returns policy. You cannot try underwear on, and some brands accept nothing once worn.
And a leg band that grips without digging, which is the thing most brands get wrong. Runderwear use silicone grippers, we use a wider band and a longer leg. Both approaches work.
Fabric, honestly
Technical synthetics dry fastest and are what you want for high-output running or anything where you will be soaked. They hold odour more than natural fibres, which is the trade.
Bamboo viscose is soft, breathable and moves moisture rather than holding it. Good for weights, classes, walking, moderate cardio. Needs a cool wash and no fabric softener.
Cotton absorbs and holds. Fine for a gentle session, poor for anything sweaty.
Merino is excellent and expensive.
Where we sit: for the gym, bamboo viscose is a strong choice. Breathable, cool, and it moves sweat rather than sitting in it. For a long summer run, a technical synthetic will dry faster, and our running comparison says so.
Getting the length and size right
This is what decides whether long-leg underwear works for you when you are moving, and it is worth two minutes before you buy.
Take the 9 inch if you are active. The 6 inch sits mid-thigh and is ideal for everyday wear. The 9 inch sits just above the knee, so there is less distance for movement to shift it. If you are doing classes, long walks or anything on a mat, take the 9.
Today I've been on an 11 mile hike in the Peak District and I didn't have to fuss with them once. They never rolled up under my trousers and the waistband was unnoticeable.
Phillippa, UK, verified review
Size up if you are between two. These work through full contact with the skin. A tighter leg has to stretch further and grips less evenly, so sizing down makes bunching more likely rather than less.
Being a size 16-18, horse riding 5/6 days a week, walking more than 18,000 steps a day. Soft, super comfortable, stretchy, breathable and ZERO CHAFFING. Just ordered 5 more.
A.R., UK, verified review
Get both right and they stay where you put them. If the first pair is not right, we swap your whole order free.
Under leggings
Fitted leggings are the hardest test for any underwear, so it is worth knowing what to expect.
A longer leg usually shows less than a brief, because the seam runs under the curve of the buttock rather than straight across it. Under very thin or very light leggings, though, any edge can show, whatever you are wearing.
If a completely invisible line is your priority, a genuinely seamfree brief from Boody or a 360 degree seamless pair from Runderwear will beat ours. If chafing is the problem you are solving, the longer leg is worth the trade, and in a mid-weight legging it will not show.
What we make
Bamboo viscose boxer shorts with a 6 or 9 inch leg, UK 8 to 30, every size one price. Wide flat waistband, smooth seams, no tag, dyed to OEKO-TEX Standard 100.
For the gym, take the 9 inch, and size up if you are between two.
Great for exercise. Bought for marathon training and have been brilliant.
Emily, UK, verified review
They come to a good length to prevent chafe and are a lot cooler than my sports shorts.
Georgia, UK, verified review
60 day comfort guarantee, free swap on your whole first order, free UK delivery. See the range.
Questions
What underwear should I wear to the gym?
Something with a leg long enough to stop thighs rubbing, a flat waistband that does not sit where your leggings' band sits, and a fabric that moves moisture rather than holding it. For most sessions that means a 6 to 9 inch boxer short or a technical brief.
What is the best gym underwear for women?
For hard cardio and running, Runderwear's recycled polyamide dries fastest. For classes, weights, walking and hot rooms, a long-leg bamboo viscose short is more comfortable. For no visible line under very fitted leggings, a seamfree brief from Boody. It depends on what you are actually doing.
Should you wear underwear under gym leggings?
Most people do, and it is largely preference. Many leggings have a built-in gusset and are designed to be worn without. If you do wear something, a flat-seamed longer leg shows less than a brief and stops thighs rubbing.
What underwear does not show under leggings?
Seamfree briefs and thongs show least. A flat-seamed boxer short usually shows less than a standard brief, because the seam sits under the curve rather than across it. Under very thin leggings, any edge can show.
Why does my underwear ride up at the gym?
Usually leg length or size. A short leg has more thigh to travel across, and underwear that is too small has to stretch further and grips less evenly. A 9 inch leg and sizing up both fix it. Some brands use silicone grippers on the hem to do the same job.
Is bamboo underwear good for the gym?
Yes. It is breathable, it keeps you cool, and it moves moisture rather than absorbing it, which is why customers use it for classes, weights, hiking and walking. For high-output running in summer, a technical synthetic dries faster.
Does cotton underwear work for exercise?
Not well. Cotton absorbs sweat and holds it, so it stays damp. Fine for a gentle session, unpleasant for anything sustained.
What stops thigh chafing at the gym?
Coverage. A smooth layer between your thighs so they glide rather than catch, with a leg long enough to reach where they actually touch. We cover the mechanics on our anti-chafing shorts page.
