Wool can absorb roughly 30–40 percent of its weight in moisture without feeling wet to the touch, explained Diana Tuulik, a materials science expert and lecturer at Tallinn University of Applied Sciences (TTK).

That trapped moisture also actually releases heat, helping keep wool garments warm even when damp. This makes wool ideal not just for outdoor enthusiasts but also baby clothes, keeping infants stably comfortable and warm in varying conditions.

From sheep to alpaca, all wools are insulating, Tuulik said, regardless of the animal source.

"If we want to compare warmth, we should focus not on the fiber itself but the fabric made from the fibers," she explained. Thickness, density and the material's ability to trap still air are what ultimately determine how warm a garment will feel.

And it's that trapped air that is key: the more air trapped between the fibers, the less heat escapes. Wool's natural crimp locks in air, which is why it's so popular for staying warm in cold conditions.

Merino wool, from a fine-fiber sheep breed of the same name, has become especially popular over the years. Soft and lightweight, merino can be worn directly against the skin, making it a suitable choice for base layers such as long underwear.

"It's often hard to believe it's even wool at all," Tuulik said. Its softness doesn't sacrifice warmth, however, because the fiber still traps enough air.

Mid- and outer layers typically use coarser wool, creating thicker, denser fabrics better at blocking wind and cold. Coarser wool is naturally water-repellent, the materials expert noted, though this can be affected by modern finishes meant to make it softer for comfort.

Wool is also naturally dirt-resistant. Tuulik advised following care labels when washing: hand wash or use a gentle machine cycle to minimize shrinkage.

Aging wool isn't necessarily a drawback, however, as older wool can become denser and even warmer over time.

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