What are natural fibers?

Natural fibers are derived from plants and animals, not from petroleum. Cotton comes from the cotton plant. Wool comes from sheep. Linen comes from flax. Silk comes from silkworms. Unlike synthetic fibers — polyester, nylon, acrylic — natural fibers biodegrade at end of life and do not shed microplastic particles when washed.

Why it matters

A single wash cycle releases between 100,000 and 6.3 million microplastic fibers per kilogram of synthetic textile. These fibers are too small for water treatment to fully capture. Researchers have now found microplastics in 8 of 12 human organ systems, including cardiac tissue and brain tissue. Natural fibers do not contribute to this. Read more about what we filter for.

Natural fibers

Cotton
The most widely used natural fiber. Breathable, soft, and biodegradable.
Linen
Made from the flax plant. The most breathable natural fiber for warm weather.
Wool
From sheep fleece. Temperature-regulating and naturally odor-resistant.
Merino
Fine wool soft enough to wear against skin. The standard for natural fiber activewear.
Hemp
From the flax plant stalk. One of the strongest and most durable natural fibers.
Alpaca
From Andean alpacas. Hypoallergenic, warmer than wool, and exceptionally soft.
Silk
From silkworm cocoons. Smooth, lightweight, and temperature-regulating.
Cashmere
From cashmere goat undercoat. Among the finest and softest natural fibers.
Jute
Plant fiber used in bags, rugs, and home goods. Biodegrades rapidly.
Sisal
From the agave plant. Exceptionally durable, used in rugs and floor coverings.

Wood-based fibers

These fibers come from wood pulp, not petroleum, but they are made with chemical processing and are not natural fibers. Some brands in the directory use them alongside natural fibers.

TENCEL Lyocell
From wood pulp using a closed-loop process. Not petroleum-derived.
TENCEL Modal
From beech wood pulp. Exceptionally soft, used in basics and underwear.

Common questions

Do natural fibers shed microplastics?
No. Natural fibers do not contain synthetic polymers and do not shed microplastic particles when washed. Synthetic fibers — polyester, nylon, acrylic — shed millions of microplastic fibers per wash cycle.
What is the most breathable natural fiber?
Linen is the most breathable natural fiber. Its loose weave structure allows more airflow than cotton, wool, or any other natural fabric.
What natural fiber is best for activewear?
Merino wool is the standard for natural fiber activewear. It is odor-resistant, temperature-regulating, and requires no chemical treatments to perform.
What is the softest natural fiber?
Cashmere is widely regarded as the softest natural fiber, followed by fine merino and alpaca. All three can be worn directly against the skin.
Is TENCEL a natural fiber?
No. TENCEL is a brand name for lyocell and modal, wood-based fibers made by chemically processing wood pulp. They are not made from petroleum like polyester, but they are not natural fibers like cotton or wool either. Brand pages tag them separately.