Bamboo vs Modal vs Cotton: What's Best for Underwear?
If you've shopped for underwear lately, you've seen these three words everywhere: bamboo, modal, cotton. All three get sold as "soft", "breathable" and "sustainable", and honestly the labels start to blur. We get asked about this a lot, so here's the proper breakdown: what these fabrics actually are, how they're made, and which one makes sense for underwear.
Spoiler: it isn't simply "bamboo is natural, so bamboo wins". It's more interesting than that.
First, a myth-buster: "bamboo fabric" usually isn't just bamboo
This is the part that trips most people up. When you read "bamboo" on a clothing label, you probably picture the plant being turned into thread. That's not what's happening.
Bamboo is a woody grass, and raw bamboo fibre (the mechanically processed kind, sometimes called bamboo linen) is coarse, closer to linen than to the silky fabric you've felt on clothing. To get that soft, drapey feel, manufacturers dissolve bamboo pulp in chemicals and re-spin it into fibre. That process is called viscose, or rayon, and the conventional version typically uses sodium hydroxide and carbon disulfide, chemicals that can pollute air and waterways if they aren't properly recovered and treated.
So most "bamboo" underwear on the market is technically bamboo viscose, not bamboo in any raw sense. This isn't a fringe complaint. In the US, the Federal Trade Commission has taken repeated action over it, with retailers agreeing to civil penalties totalling roughly 1.26 million dollars in 2013, 1.3 million in 2015, and 5.5 million in 2022 (that last one involving Kohl's and Walmart). The FTC's position is simple: once bamboo is chemically processed, the finished fibre is rayon, so it has to be labelled "rayon" or "rayon made from bamboo", not just "bamboo". The FTC has also separately challenged "antibacterial" and "eco-friendly" bamboo claims as unproven.
None of this makes bamboo viscose bad to wear. It's soft, it breathes, and plenty of people love it. But if sustainability is the reason you're reaching for it, the word "bamboo" alone doesn't tell you much about how it was actually made.
So what is modal, exactly?
Modal is also a regenerated cellulose fibre, meaning it goes through a dissolve-and-respin process like bamboo viscose, but it's made from beech tree pulp, and the better versions are made under much tighter environmental controls.
The name you'll see most is TENCEL™ Modal, made by the Austrian company Lenzing. Here's a distinction worth getting right, because a lot of articles get it wrong. You may have read that "modal recovers over 99% of its solvents in a closed loop". That famous figure actually belongs to TENCEL™ Lyocell, a different fibre made with a non-toxic solvent in a genuinely closed loop. TENCEL Modal is made with a modified viscose process instead: cleaner than generic viscose, using oxygen-based bleaching and recovering a high share of its process chemicals (Lenzing has cited around 95%), but it isn't the same near-zero-waste loop as Lyocell. The honest short version: TENCEL Modal is a cleaner, more transparent modal than the generic kind, with real numbers behind it, rather than a miracle fabric.
Beech trees are also low-maintenance to grow. They're largely sourced from managed forests in Central Europe and don't need irrigation or replanting the way many crops do.
On feel, modal is one of the softest apparel fibres there is: smoother and silkier than cotton, with a bit more stretch. It's also good at moisture: it absorbs sweat and releases it into the air faster than cotton, so it feels drier and cooler against the skin rather than staying damp. That matters a lot for something worn against your body all day.
And cotton, the fabric everyone already knows
Cotton barely needs an introduction, but it's worth remembering it's a completely different category. It's a natural fibre, harvested from the cotton plant and spun straight into thread, with no chemical dissolving step. That simplicity is part of why cotton has been a wardrobe staple for so long.
Cotton is breathable, gentle on sensitive skin and widely considered hypoallergenic, which is why it's stayed a go-to for underwear. Its trade-off shows up with moisture: cotton absorbs sweat but holds onto it, so on hot or active days it can stay damp longer than modal, which releases moisture faster. Cotton also tends to lose its shape and softness a bit faster over many washes, where modal resists pilling and stretching better.
On the environmental side, cotton is genuinely resource-heavy. WWF estimates it takes around 2,700 litres of water to produce a single cotton t-shirt, roughly what one person drinks in about two and a half years. Beech, the raw material for modal, needs no irrigation and far less water. Organic cotton improves on the chemical side, but it's still a thirstier crop than beech.
Putting it side by side
Feel. Modal tends to win, silkier and smoother than both cotton and bamboo viscose, though good bamboo viscose comes close.
Breathability and moisture. All three breathe reasonably well, but modal moves moisture away and dries faster, rather than just absorbing and holding it like cotton.
Durability. Modal holds its shape and resists pilling better than cotton over time. Cotton tends to thin out and lose structure faster with repeated washing.
Sustainability. The most nuanced one. Beech for modal needs very little water or land management, and the better modal processes recover most of their chemicals. Bamboo as a raw crop is fast-growing and low-input, but bamboo viscose processing is often not closed-loop, so a lot of that raw sustainability gets undone in manufacturing. Cotton is the most water and land intensive of the three, especially when it isn't organic.
Everyday comfort for underwear. This is where modal has the edge, because the combination of softness, faster-drying comfort and shape retention matters more for something worn against skin all day than it does for a t-shirt.
Why this matters for what you're wearing
We're not here to tell you cotton is bad or bamboo viscose is a scam. Both are perfectly reasonable choices, and plenty of great underwear is made from each. But "natural", "eco" and "bamboo" get thrown around so loosely in fashion marketing that it's genuinely hard to know what you're buying without digging in.
That's a big part of why we make our undies from modal spun from sustainably sourced beechwood. It's not just the softness, although yes, it's extremely soft. It's that beech is a low-water, renewable source, and modal gives you that silky, faster-drying, holds-its-shape comfort that works so well against skin all day. If you've been choosing fabrics by which label sounds the most "natural", it might be worth choosing by what's actually happening in the supply chain instead. Sometimes the more processed option is the more transparent one.
You'll find the same beechwood modal across the range, from our 3″ boyleg briefs and 5″ boxer briefs to the 8″ biker shorts and our loungewear. Prefer classic cotton? We make that too.
Frequently asked questions
Is bamboo underwear actually made from bamboo?
Technically yes, but not the way most people picture. The bamboo plant is dissolved into pulp and chemically re-spun into fibre, a process called viscose. So bamboo is the raw material, but what ends up on your body is rayon, made the same way as most rayon fabrics. The FTC has taken action against brands for labelling this simply "bamboo" rather than "rayon made from bamboo".
Is modal natural or synthetic?
Neither exactly, it sits in between. Modal starts from a natural, plant-based source (beech pulp) but goes through chemical processing to become fibre, which is why it's classed as semi-synthetic, or "regenerated cellulose". It isn't petroleum-based like polyester or nylon, but it isn't a raw natural fibre like cotton either.
Is modal better than cotton?
It depends what you're optimising for. Modal generally wins on softness, faster-drying comfort and holding its shape over time, resisting pilling and stretching better than cotton. Cotton wins on simplicity, since it's a raw fibre with no chemical processing, and it's a safe choice for sensitive skin. For underwear worn all day or on active days, most people find modal the more comfortable option.
Does modal shrink?
Not easily. Modal is more shrink-resistant than cotton, but it isn't shrink-proof. High heat, hot water or a hot dryer, is the main culprit, so wash cold and air dry or tumble on low to keep it looking new.
Is modal biodegradable?
The fibre is. TENCEL™ Modal is certified by TÜV Austria as biodegradable and compostable, since it's made from cellulose rather than plastic-based fibres. One thing to know: most underwear is blended with a little elastane for stretch, and that blend won't fully biodegrade the way 100% modal would.
Why does modal feel cooler than cotton?
It comes down to how each fabric handles moisture. Cotton absorbs sweat and holds onto it, which can feel damp. Modal absorbs moisture too but releases it into the air faster, so it feels drier and cooler even when you're warm. That's part of why it's such a popular choice for underwear.