These two fabrics account for most of what's in your wardrobe, and the honest comparison isn't "which is better" — each wins clearly at different jobs. Cotton is more breathable, softer, and more comfortable but absorbs moisture and holds it; polyester wicks moisture and is far more durable but traps odour — which is why so much clothing is now a blend.
The fundamental difference
Everything follows from this. Cotton is a natural fibre that's hydrophilic — it absorbs water. Polyester is a synthetic that's hydrophobic — it repels water, so moisture travels along the fibre surface and evaporates rather than soaking in. That single property explains nearly every practical distinction: why cotton feels comfortable but heavy when sweaty, why polyester dries fast but can feel clammy, and why performance apparel is overwhelmingly synthetic while everyday tees are cotton.
Breathability and comfort: cotton wins
Cotton is more breathable, generally softer against the skin — especially combed ring-spun cotton, which improves with washing — and less likely to irritate sensitive skin. Polyester, being plastic-derived, is less breathable and can feel clammy in humidity or when you're not moving enough for wicking to work. For lounging, everyday wear, and general comfort, cotton is simply more pleasant against your body, which isn't a small consideration.
Moisture and durability: polyester wins
Moisture management — polyester wicks sweat to the surface to evaporate, while cotton absorbs it and becomes heavy, cold, and clinging. That's the entire reason performance kit is synthetic. Durability — polyester is stronger, more abrasion-resistant, and holds shape far better, resisting shrinking, stretching, and wrinkling. Colour retention — synthetic dyes bond well, so it fades less. Drying time — dramatically faster. For sweat, repeated washing, or hard wear, polyester wins clearly.
The odour problem (polyester's real weakness)
The genuine downside, and a significant one. Polyester holds smell far more stubbornly than cotton — odour-causing bacteria adhere readily to synthetic fibres, and body oils bind to the hydrophobic surface, so a polyester shirt can smell after one session and retain a lingering odour even after washing. Cotton, being absorbent, releases odour more completely in the wash. It's why gym kit develops a permanent funk that regular tees don't — see washing gym clothes.
Care, cost, and environment
Care — polyester resists wrinkles, dries fast, and barely shrinks, while cotton wrinkles and shrinks with heat. But polyester is more heat-sensitive, so low dryer heat matters. Cost — polyester is cheaper to produce, which is why it dominates fast fashion. Environment — honestly neither is clean: cotton is water- and pesticide-intensive, polyester is petroleum-derived, non-biodegradable, and sheds microplastics. Recycled polyester and organic cotton are partial improvements. There's no straightforwardly virtuous option.
Why blends exist (and where triblend sits)
Cotton-polyester blends capture cotton's comfort alongside polyester's durability and shape retention — a genuine compromise rather than a fudge. Triblend adds rayon for drape, producing an unusually soft, lightweight fabric that's a comfort and style choice rather than a performance one. Honest summary: cotton for comfort, polyester for performance and durability, blends for most everyday clothing, technical synthetics for heavy sweat. See also triblend vs cotton.
Quick answers
Is cotton or polyester better?
Neither universally — cotton for comfort and breathability, polyester for moisture-wicking and durability.
Which for working out?
Polyester or technical synthetic, because it wicks rather than absorbs.
Which is more comfortable?
Cotton.
Which lasts longer?
Polyester.
Why does polyester smell?
Bacteria and body oils bind readily to synthetic fibres and wash out less completely.
Which shrinks?
Cotton with heat; polyester is heat-set and barely shrinks.
Why are blends common?
They combine cotton's comfort with polyester's durability.
Cotton drinks your sweat and polyester moves it. Everything else about the comparison follows from that one difference.
Cotton absorbs moisture and polyester repels it, which explains why one is more comfortable and the other performs better when you're sweating. Cotton wins on breathability, softness, and odour; polyester on moisture, durability, and drying time. Blends exist because most clothing needs both — and for heavy sweat, technical synthetic is still the right tool.