Most clothes thrown into landfills don’t simply disappear. Natural fibers like cotton break down slowly over decades, producing methane in the process, while synthetic fabrics like polyester can persist for centuries, fragmenting into tiny plastic particles. What happens depends almost entirely on what the garment is made of.
Natural Fibers Break Down Slowly and Produce Methane
Landfills are designed to entomb waste, not decompose it. Most are managed as “dry tombs,” where the goal is to minimize moisture getting into the waste mass. That means even biodegradable materials break down far more slowly than they would in a backyard compost pile. Cotton textiles in an average landfill have a decay rate roughly five times slower than food waste under the same conditions, according to EPA modeling data. In a dry landfill, cotton can take well over 100 years to fully break down. Even in wetter conditions, reaching 95% decomposition still takes decades.
The decomposition that does happen occurs without oxygen, since buried waste is sealed under layers of other trash and soil. This anaerobic process is fundamentally different from composting. Instead of producing carbon dioxide and nutrient-rich soil, it generates methane, a greenhouse gas roughly 80 times more potent than CO2 over a 20-year period. Cellulose-based fibers like cotton and linen are particularly efficient methane producers because bacteria can break apart the cellulose bonds relatively easily, releasing acetate that feeds gas-producing microorganisms.
Wool and silk also decompose anaerobically, and research has found they can produce surprisingly high methane yields under certain conditions. The proteins in these fibers, keratin in wool and fibroin in silk, undergo structural changes as microbes work on them. So even “natural” clothing contributes to landfill greenhouse gas emissions, sometimes substantially.
Synthetic Fabrics Barely Decompose at All
Polyester, nylon, acrylic, and other petroleum-based fabrics are essentially plastics shaped into thread. Landfill microbes have no meaningful ability to break them down. A polyester shirt buried today will still be largely intact centuries from now. But “intact” is misleading, because these fabrics don’t just sit there inertly. Over time, physical stresses, temperature changes, and chemical exposure cause them to fragment into smaller and smaller pieces.
Those fragments become microplastics, tiny plastic particles that work their way into the surrounding soil and leachate (the liquid that percolates through landfill waste). The United Nations University has noted that synthetic textiles in landfills can persist for hundreds of years while continuously fragmenting into microplastics. These particles have been found in terrestrial soils around landfill sites, where they affect soil health and agricultural productivity. They also travel through leachate into groundwater systems, carrying the issue well beyond the landfill’s boundaries.
Chemicals Leach Into Soil and Water
The fabrics themselves are only part of the problem. Modern clothing is loaded with chemical treatments: dyes, flame retardants, water-repellent coatings, antimicrobial finishes, and plasticizers. As rainwater filters through landfill waste, it picks up these chemicals and carries them downward as leachate.
Heavy metals are among the most concerning contaminants. Chromium is especially common because it’s widely used in leather tanning. Zinc compounds show up frequently in synthetic materials, where they serve as thermal stabilizers, antimicrobial agents, flame retardants, and pigments. Research using atomic absorption spectrometry has detected chromium, copper, zinc, arsenic, cadmium, and lead in extracts from textiles and leather goods. Other metals found in textile-related materials include cobalt, mercury, nickel, barium, and aluminum.
Synthetic dyes pose their own risks. Studies have shown these dyes have toxic and genotoxic effects on aquatic organisms. When leachate carrying dissolved dye compounds reaches waterways, it can disrupt ecosystems downstream. The chemicals used in dyeing and finishing processes, not just the dyes themselves, add to this chemical cocktail. Zinc sulfide used as a pigment, chromium(III) salts from tanning, and various compounds from plastic production all contribute.
Blended Fabrics Create a Worst-of-Both-Worlds Scenario
A large share of modern clothing is made from blended fabrics, like a cotton-polyester T-shirt. These garments partially decompose as bacteria attack the cotton fibers, producing methane and leaving behind a weakened mesh of synthetic threads. That synthetic remnant is more prone to fragmenting into microplastics than a solid polyester garment would be, because the decomposition of the natural fibers creates more surface area and structural instability. You get the methane emissions from the natural component and the microplastic pollution from the synthetic one.
Bioreactor Landfills Speed Things Up, But Only for Natural Fibers
A small number of landfills operate as bioreactors, deliberately adding moisture to the waste mass to accelerate decomposition. EPA research has found that bioreactor cells decompose waste several times faster than conventional dry-tomb cells. For cotton textiles specifically, the decay rate in a bioreactor is roughly six times faster than in a dry landfill.
That acceleration matters for gas capture. Faster decomposition means methane is produced over a shorter, more concentrated period, making it easier to collect and convert to energy rather than letting it escape into the atmosphere. But bioreactor technology does nothing for synthetic fabrics. Polyester in a bioreactor landfill is just as persistent as polyester in a dry one. And the vast majority of landfills in the United States still operate as dry tombs under federal regulations, so even the natural-fiber benefit is limited to a handful of sites.
The Scale of the Problem
What makes all of this significant is volume. The EPA estimates that millions of tons of textiles reach U.S. landfills each year, and global figures are far larger. Each buried garment represents a small but compounding source of methane, chemical leachate, or microplastic pollution, depending on its fiber content. Unlike food waste, which decomposes relatively quickly (even in a landfill), clothing waste occupies a middle ground where natural fibers decay slowly enough to produce methane for decades, and synthetic fibers essentially never go away.
The practical takeaway is that landfills don’t make clothes disappear. They preserve synthetics almost indefinitely while slowly converting natural fibers into greenhouse gases. The dyes, finishes, and chemical treatments on both types leach into the surrounding environment for as long as the materials remain. Donating, reselling, or repurposing clothing keeps it out of this cycle entirely, which is why textile diversion programs have a measurable environmental impact that goes well beyond just reducing landfill volume.