Lesson · Hot weather

What keeps you cool is a fiber that soaks up sweat and lets it dry. Fiber scientists measure this as moisture regain: how much water a fiber holds from the air.

• The best: linen and hempThey absorb moisture (about 12%) and dry fast, and the loose weave lets air through. Linen is also stronger when wet. Skin & comfort: A.
• Also good: lyocell, viscose, modal, cotton, silkLyocell holds about 11.5%, viscose 11–13%, silk 11% and cotton 8.5%. All feel cool and soft. In heavy humidity, cotton dries more slowly than linen. Viscose vs modal vs lyocell · More on cotton
• Wool in summer?Fine merino wool absorbs the most (up to 18%) and handles sweat well. But it’s warm, so it’s better for active or changeable weather than for a heat wave.
• Avoid in the heat: polyester, acrylic, nylonPolyester holds only 0.4% moisture and acrylic 1.5%, so sweat stays on your skin. “Moisture-wicking” synthetics spread sweat out so it dries faster, which helps during sport. But they still absorb almost none, and they shed microplastics. More on microplastics
• Fit and weave matter tooLoose shapes and light, open weaves let air move: linen, cotton voile, seersucker. A tight, thick weave feels hot even in a good fiber.
• Is linen good for hot weather?Yes. It’s the best of the fibers we grade and the most sustainable: #1 in our Fabric Ranking, with hemp right behind. More on linen
• Moisture and skin gradesLinen, hemp: about 12% · A
  Lyocell: about 11.5% · A
  Viscose, modal: about 11–13% · A
  Silk: about 11% · A
  Cotton: 8.5% · A
  Nylon: 4–4.5% · D
  Acrylic: 1.5% · D
  Polyester: 0.4% · D
  How we grade · Check a piece with the Clothing Check

Sources: Shuvo 2020, fiber properties · ASTM D1909, standard moisture regain · Alliance for European Flax-Linen & Hemp