Linen
A bast-fiber fabric made from flax. Lightweight, breathable, and naturally cooling — the warm-climate workhorse. Wrinkles immediately and aggressively.
Linen comes from the flax plant — a bast fiber, meaning it's harvested from the stalk rather than a seed pod (cotton) or animal coat (wool). The fibers are hollow, which makes the fabric naturally moisture-wicking and dramatically cooler than cotton at the same weight. A linen shirt in 95°F humidity feels like an open window; a cotton shirt at the same temperature feels like a damp towel.
The cost is wrinkle-resistance — linen wrinkles aggressively and the wrinkles set fast. Most linen wearers eventually accept the lived-in look as part of the deal; the alternative is steaming every morning. Some modern blends (linen-cotton, linen-rayon) trade some breathability for less wrinkling but the pure version is what makes hot weather bearable.
Quality variation: Belgian and Italian linen (longer fibers, looser weaves) is dramatically softer and more drapey than the cheaper, stiffer linens common in fast-fashion summer pieces. The number to look for is "yarn count" or "Lea count" — higher counts = finer yarns. Most decent shirting linen is around 50 Lea; very fine linen runs 80+.
Weight: 100–180 GSM is standard for shirting. Anything heavier starts to feel like canvas. Anything lighter is borderline transparent.