The short answer. Both are breathable and both are good choices. Cotton is a spun natural fiber that is more durable, easier to launder and more textured against the skin. Viscose derived from bamboo is a smoother regenerated fiber with a heavier drape that hangs away from the body and feels cooler on first contact. If you want something that lasts through rough laundering, choose cotton. If you want something that feels cool the moment it touches you and looks more like clothing than nightwear, choose bamboo viscose.
What each fabric actually is
Cotton is a natural fiber picked from a plant and spun into yarn. The fibers are short and they sit at slightly different angles, which is what gives cotton its matte look and its faint texture against skin.
Viscose derived from bamboo is a regenerated fiber. Bamboo is broken down into pulp and then reformed into long smooth filaments. This is why it is correctly called viscose derived from bamboo rather than simply bamboo. The finished fabric shares very little with the plant it started as, and any brand describing it as raw bamboo is being loose with the truth.
How each one handles moisture
This is the question that matters if you overheat. Both fibers are absorbent, which means they take moisture into the fiber itself rather than letting it sit on the surface. That is why both feel better than polyester when you are damp.
The practical difference is surface texture. A smooth filament makes continuous contact with the skin and conducts heat away from it efficiently, which is the reason bamboo viscose registers as cool when you first put it on. Cotton has more air trapped in its surface and reads as neutral rather than cool. Once both are genuinely wet the advantage narrows considerably, and neither fabric will keep you dry through a heavy night sweat. What they do is stop you feeling clammy for longer than a synthetic would.
How each one drapes
Drape is underrated and it does real work. Bamboo viscose is heavier for its thickness and falls away from the body rather than resting on it. That gap between fabric and skin is where air moves, and moving air is what carries heat off you. Cotton jersey is lighter and tends to follow the shape of the body more closely, which is comfortable but leaves less of that margin.
Drape is also why bamboo viscose reads as clothing rather than nightwear. A fabric that hangs like this looks intentional, which is the reason Kuula builds loungewear from it instead of confining it to a bedroom.
Where cotton wins
Cotton is more robust wet. Viscose fibers lose strength when saturated, which is why bamboo viscose garments ask for gentler laundering and a mesh bag. Cotton tolerates a hot wash and a hot dryer in a way viscose does not. Cotton is also cheaper to produce, so a cotton set at the same price point is usually the less considered garment of the two.
Where bamboo viscose wins
It feels cooler on contact. It drapes rather than clings. It is smoother against skin that feels reactive, because there are fewer short fiber ends standing up from the surface. It holds color with more depth. The honest tradeoff is that it wrinkles more readily and it needs a gentler wash.
What about the sustainability claims
Bamboo grows quickly and needs little irrigation, which is a genuine advantage at the farming stage. Turning it into viscose is a chemical process, and how responsibly that is done varies enormously between producers. Be skeptical of any brand making sweeping environmental claims about bamboo fabric without naming the process or a certification behind it. Kuula describes its fabric as viscose derived from bamboo because that is what it is, and holds no third party environmental certification at this time.
How to choose
Choose cotton if you launder hot, if you are hard on clothes or if you dislike the feel of anything slippery. Choose viscose derived from bamboo if the first moment of contact matters to you, if you want something that hangs well enough to wear beyond the house, or if your skin objects to texture. Many women who run warm end up owning both and reaching for the bamboo viscose on the worst nights.
Kuula cuts every piece from a fabric that is 94% viscose derived from bamboo and 6% spandex. The spandex is there so the fabric recovers its shape rather than growing through the evening. You can see how it behaves on the Nightie or the Bamboo Lounge Pant, and the DreamCare Laundry Bag exists because viscose asks for a gentler wash.
Frequently asked questions
Is bamboo viscose cooler than cotton?
It usually feels cooler on first contact because the fiber is smooth and conducts heat away from the skin efficiently. Once both fabrics are genuinely wet the difference narrows. Both are far more breathable than polyester.
Is bamboo viscose the same as bamboo?
No. Bamboo is broken down into pulp and regenerated into fiber through a chemical process. The accurate description is viscose derived from bamboo, and any label claiming pure bamboo fabric is overstating things.
Does bamboo viscose wrinkle?
Yes. It wrinkles more readily than cotton. That is the tradeoff for the drape and the softness.
How should I wash bamboo viscose?
Wash cool on a gentle cycle inside a mesh bag, then tumble dry low or hang to dry. Viscose loses strength when wet, so it needs more care than cotton does.
Which is better for night sweats?
Neither will keep you dry through a heavy night sweat. Both beat synthetics. Bamboo viscose tends to feel less clammy afterwards because of its drape and its smooth surface.
Related reading: what cooling loungewear is and how to choose it and what to wear during hot flashes.