What fabrics are biodegradable?
Whether a fabric biodegrades depends on what it is made from. Natural fibers — cotton, wool, linen, silk, hemp, alpaca, cashmere — come from plants and animals and are composed of cellulose or protein. Both break down in soil through microbial decomposition. Synthetic fibers — polyester, nylon, acrylic — are made from petroleum and are plastic at a molecular level. They do not biodegrade. They persist in the environment for hundreds of years and fragment into microplastics that enter soil, waterways, and eventually food systems.
Fully biodegradable: natural fibers
Wool, linen, cotton, silk, hemp, alpaca, and cashmere are all fully biodegradable under natural conditions. Wool is a protein fiber (keratin) that decomposes in soil within months, releasing nitrogen and sulfur as nutrients. Cotton, linen, and hemp are cellulose-based plant fibers that break down readily in composting conditions. Silk — another protein fiber — biodegrades within a few years. Alpaca and cashmere behave like wool. None of these fibers produce microplastics during decomposition or washing. In undyed, unfinished form, these fibers can be composted at home alongside food scraps.
Semi-natural: TENCEL, lyocell, and modal
Fibers like TENCEL (a brand of lyocell), modal, and viscose are made from natural cellulose — usually wood pulp — but are chemically processed to create the fiber. They occupy a middle ground. TENCEL and lyocell are certified biodegradable under industrial composting conditions, and TENCEL specifically is produced in a closed-loop process that recovers and reuses most of the solvent used to dissolve the wood pulp. Viscose (also called rayon) uses more aggressive chemicals and has a less clean biodegradation profile. None of these are purely natural fibers, and they should not be confused with the plant fibers they are derived from.
Synthetics do not biodegrade
Polyester, nylon, and acrylic are plastic fibers. A polyester garment in a landfill will persist for 200 years or more. Rather than decomposing, synthetic fibers fragment into progressively smaller particles — microplastics — that are too small to be visible but are present throughout the environment. Microplastics have been found in Antarctic ice, deep ocean sediment, human blood, and breast milk. There is no natural biological process that breaks synthetic polymer fibers into harmless compounds within any relevant timeframe.
The dye and finish caveat
Even a natural fiber garment may biodegrade slowly if it is treated with synthetic dyes, chemical water-repellent finishes, flame retardants, or anti-shrink coatings. These treatments bind to the fiber and can inhibit microbial decomposition or release harmful compounds as they break down. A GOTS-certified natural fiber garment — dyed and finished without prohibited chemicals — will biodegrade far more cleanly than a conventionally processed natural fiber one. If end-of-life biodegradability matters to you, certification provides more assurance than fiber content alone.
Why this matters beyond landfill
The biodegradability question is not only about what happens to garments at the end of their life. Microplastic shedding during washing is a separate issue: synthetic fabrics release hundreds of thousands of microplastic fibers per wash cycle into wastewater. Wastewater treatment plants capture some of these, but a significant fraction passes through into rivers and oceans. Natural fibers shed fibers too when washed, but those fibers are protein or cellulose-based and break down in the environment rather than persisting and accumulating. Every load of synthetic laundry contributes to an environmental problem that does not have a simple downstream solution.