Head-to-head comparisons for common buys: what the research says on odor, moisture, warmth, durability, microplastics, cost and care. Every row is sourced, and each page says where the synthetic option is the better choice.
Merino holds less odor and isn’t plastic, so it doesn’t add plastic fibers when it sheds. Polyester dries faster, costs less and, in one survey, lasted longer. For warmth, studies find little difference between the two.
Cotton tees held less odor in exercise studies and break down in soil and water; polyester tees dry faster and, in one survey, lasted longer. For comfort in heat, studies found no difference.
Fleece dries faster, often costs less and, in one survey, lasted longer. Wool holds less odor, doesn’t melt and isn’t plastic, while polyester fleece sheds plastic microfiber in the wash. For warmth, thickness and construction matter more than fiber.
Wool-rich socks hold less odor, but nearly all of them contain nylon for wear, so “wool sock” usually means a blend. Chemicals in socks follow processing more than fiber.
Comparisons summarise published studies and product labels; they are not scores or product ratings. Several studies were funded by fiber industries, and each page says which. See also Why the label matters.