Polyester resists decomposition for decades and likely much longer. Under typical landfill or soil conditions, 100% polyester fabric shows essentially no measurable biodegradation even after months of burial, and realistic estimates for full breakdown stretch well beyond a human lifetime. The commonly cited range of 20 to 200 years is more of an educated guess than a hard measurement, because no one has actually watched a polyester shirt decompose start to finish under natural conditions. What researchers have documented is that polyester does not sit quietly while it persists: it fragments, sheds microplastics, and slowly changes at the molecular level in ways that matter for ecosystems and human health.
What Happens to Polyester in Soil and Landfills
The most straightforward answer about polyester decomposition comes from burial studies, and the results are blunt. In a direct comparison of cotton and polyester fabrics in soil, cotton and recycled-cotton fabrics degraded by 93 to 95 percent within one month and disappeared entirely within four months. Fabrics made from 100% virgin polyester (PET) and 100% recycled polyester showed zero degradation after one, four, and seven months of soil burial.1PubMed. Soil biodegradation of virgin and recycled cotton and PET based fabrics: physicochemical and biological assessment An earlier study looking at polyester under both laboratory conditions and a compost environment found the same thing: the polyester fabric remained intact.2Journal of Engineered Fibers and Fabrics. Biodegradability Study on Cotton and Polyester Fabrics
Landfills are even less hospitable to decomposition than open soil. Modern landfills are designed to minimize moisture and oxygen penetration, which are the two things that drive biological breakdown. Polyester already resists microbial attack under ideal conditions; in the oxygen-starved interior of a landfill, the process essentially stalls. This is why so many environmental estimates place polyester decomposition at 20 to 200 years or more, but those numbers carry real uncertainty. They are extrapolated from short-term lab degradation rates, not observed in real time.
Decomposition in the Ocean
Polyester that ends up in marine environments fares slightly differently than polyester buried in dry landfill, but “slightly” is the key word. In a study that buried polyester fibers in marine sediment and tracked them over nine months, researchers found that the polyester did begin to break down both physically and chemically. Cotton threads placed alongside it had completely vanished by the six-month mark. The polyester threads showed fragmentation and deterioration, but visible fragments still persisted at nine months.3Marine Pollution Bulletin. Baseline Polyester fibres slowly degrade in marine sediments
So marine conditions can accelerate the process compared to dry burial, likely because of the combination of saltwater chemistry, microbial communities in sediment, and physical abrasion. But “accelerate” is relative. The polyester was still clearly there after nine months of burial. Extrapolating from that rate, full decomposition in marine sediment would still take many years, and floating polyester on the ocean surface or suspended in the water column faces different conditions still. Sunlight, wave action, and temperature all influence how quickly the material breaks apart, though breaking apart and truly decomposing are not the same thing.
Fragmentation Is Not the Same as Decomposition
This distinction matters enormously and is the source of most confusion around polyester’s lifespan. Polyester can fragment quickly, especially under UV light, but fragmentation just means it breaks into smaller and smaller pieces. True decomposition means microorganisms convert the material back into carbon dioxide, water, and simple organic molecules. Polyester fragments very efficiently while decomposing very slowly, which is arguably the worst combination from an environmental standpoint.
A study exposing four types of polyester fabrics to artificial UV light demonstrated this vividly. Before any weathering, the fabrics released a few hundred microfibers per gram of textile. After just two months of UV exposure, the same fabrics were shedding between 150,000 and 450,000 microplastic fibers per gram, plus an additional 10,000 to 52,000 non-fibrous microplastic particles per gram.4PubMed Central. Characterization of fiber fragments released from polyester textiles during UV weathering The fabric was physically disintegrating at an enormous rate, but each of those hundreds of thousands of tiny particles was still polyester. It had not been converted into anything benign. It had just become smaller, harder to clean up, and easier to spread through ecosystems.
Microfibers From Everyday Use
You do not need UV weathering to generate microplastics from polyester. The simple act of washing polyester clothing releases fibers into wastewater. Research comparing different washing conditions found that synthetic fabrics shed more microfibers at higher temperatures and when washed with detergent compared to water alone. The type of washing machine also made a difference: pulsator-style machines released more fibers than front-loading drum machines.5PubMed. Microfiber release from different fabrics during washing
These laundry-generated microfibers mostly end up in wastewater treatment plants, where the majority get trapped in sewage sludge rather than passing through into rivers and oceans. That sounds like good news until you consider what happens next. Most sewage sludge from treatment plants is applied to agricultural land as fertilizer, which means the microplastics move from your washing machine to the treatment plant to farm fields, where they accumulate in soil.6PubMed. Efficient Depolymerization and Low-Toxicity Leaching of Polyester Microplastics through Alkali-Hydrothermal Treatment of Sewage Sludge Since polyester barely degrades in soil, those particles stay where they land and build up over time with each new round of sludge application.
The practical takeaway: even while a polyester garment is still being worn and washed, it is slowly shedding pieces of itself into the environment. The decomposition timeline for polyester is not just about the garment as a whole but about millions of tiny fragments each on their own very long clock.
Why Polyester Is So Stubborn
Polyester’s resistance to decomposition comes down to its molecular architecture. The most common form, polyethylene terephthalate (PET), is built from aromatic ring structures connected by ester bonds. Those aromatic rings make the polymer chains pack tightly together into crystalline regions that most enzymes and microbes cannot penetrate. Biological degradation tends to start at the amorphous (less ordered) regions on the surface and works inward very slowly because the crystalline zones act as barriers.
Research on polyester-degrading bacteria illustrates the problem. In one screening study, five bacterial strains were identified that could degrade polyester fibers, but the best performers achieved only about 5 to 6 percent mass loss over 30 days. The mechanism was surface erosion: enzymes chipped away at the outer layer and broke ester bonds, but the bulk of the material remained untouched.7PubMed Central. Screening, Identification, and Degradation Mechanism of Polyester Fiber-Degrading Bacteria At that rate, full biological degradation would take years under laboratory conditions that are far more favorable than anything a polyester shirt encounters in a landfill.
Microbes That Can Break Down Polyester
Nature is not entirely helpless against polyester. In 2016, researchers reported a bacterial strain called Ideonella sakaiensis isolated from a PET bottle recycling facility. This bacterium produces two enzymes that together can break PET down into its two original building blocks, terephthalic acid and ethylene glycol, which are environmentally harmless.8PubMed. A bacterium that degrades and assimilates poly(ethylene terephthalate) The discovery was a landmark because it demonstrated that complete biological recycling of PET was at least chemically possible.9PubMed Central. Development of a Targeted Gene Disruption System in the Poly(Ethylene Terephthalate)-Degrading Bacterium Ideonella sakaiensis and Its Applications to PETase and MHETase Genes
Fungi also contribute. Certain fungal enzymes, particularly cutinases and lipases that fungi normally use for other purposes, have been shown to degrade PET in laboratory settings.10PubMed Central. Fungal Enzymes Involved in Plastics Biodegradation In nature, though, these organisms work slowly and encounter polyester in forms that are harder to attack than thin lab films. A thick polyester fleece jacket is a very different target than a carefully prepared PET sample in a warm, moist laboratory incubator.
The gap between what microbes can do under optimized conditions and what actually happens in the environment is enormous. Soil and ocean temperatures are generally too low for the enzymes to work at peak efficiency, the polyester’s crystalline structure limits access, and the microorganisms face competition for nutrients from easier food sources. This is why polyester persists in the wild despite the existence of organisms that can technically degrade it.
Engineered Enzymes and the Future of Polyester Recycling
The discovery of natural PET-degrading enzymes sparked a race to engineer faster versions. The most impressive result so far comes from an engineered variant called LCC ICCG, which converted 98 percent of PET into its component monomers within 24 hours under optimized industrial conditions.11PubMed Central. Assessment of Four Engineered PET Degrading Enzymes Considering Large-Scale Industrial Applications Researchers also managed to reduce the amount of enzyme needed by a factor of three and lower the reaction temperature, both important steps toward making the process economically viable.
This is not decomposition in the environmental sense. It is industrial enzymatic recycling, where polyester waste is deliberately processed in reactors at controlled temperatures. The output is purified monomers that can be repolymerized into new PET of the same quality as virgin material, making it a true circular recycling pathway rather than the downcycling that mechanical recycling typically produces. Several companies are now scaling pilot plants based on similar enzyme technology, though widespread commercial deployment is still years away.
For the average person wondering about the polyester clothing in their closet, enzymatic recycling does not change the decomposition timeline in nature. It offers a potential end-of-life solution for polyester that is collected and processed through purpose-built facilities. Polyester that escapes into the environment as litter, microfibers, or landfill waste will still persist for decades or longer.
What About Polyester Blends
Most polyester clothing is not 100% polyester. Polyester-cotton blends are among the most common fabrics in the world, and their decomposition behavior is not a simple average of the two fibers. Research into the thermal and chemical behavior of polyester-cotton blends has found that the two fibers interact during decomposition in ways that differ from what you would predict by just adding up their individual behaviors.12Textile Research Journal. The thermal decomposition and heat release properties of the nylon/cotton, polyester/cotton and Nomex/cotton blend fabrics
In soil biodegradation studies, blended fabrics containing recycled cotton and recycled polyester did show some degradation that depended on the cotton ratio, while pure polyester and pure recycled polyester showed none.1PubMed. Soil biodegradation of virgin and recycled cotton and PET based fabrics: physicochemical and biological assessment The cotton component degrades, which can cause the fabric to physically fall apart, but the polyester fibers within the blend persist individually. In effect, a decomposing polyester-cotton blend shirt does not vanish. The cotton dissolves and the polyester fibers scatter, creating another pathway for microplastic dispersal.
This complicates recycling as well. Enzymatic and chemical recycling processes designed for pure PET struggle with blended fabrics because the cotton and polyester need to be separated or treated with different chemistry. The prevalence of blended textiles is one of the biggest practical obstacles to closing the loop on polyester waste.
Health Concerns From Polyester Particles
As polyester fragments accumulate in the environment, they also accumulate in our bodies. Microplastics have been found in human blood, lungs, and digestive systems. The health effects are still being investigated, but early research on airway cells is not reassuring. A study exposing human and mouse lung cells to textile microplastic fibers found that polyester fibers impaired the normal development of airway lining cells, though the effects were milder than those seen with nylon fibers.13American Journal of Respiratory and Critical Care Medicine. Inhalable Textile Microplastic Fibers Impair Airway Epithelial Differentiation
The concern is not that any single polyester fiber is acutely toxic but that these particles are persistent, everywhere, and we are only beginning to understand what chronic low-level exposure does over years. Polyester’s resistance to decomposition, the very property that makes it durable and useful as a fabric, is also what makes it linger in tissues and environments indefinitely. Every year that polyester takes to decompose is another year its fragments circulate through air, water, soil, and bodies.
How Testing Standards Lag Behind the Problem
One reason the decomposition timeline for polyester remains vague is that standardized testing methods were not designed with synthetic textiles in mind. Existing biodegradation standards were developed primarily for packaging materials and bioplastics, and they measure degradation in specific environments like industrial compost, soil, or aquatic systems. A review of these methodologies found significant gaps: the standards do not adequately cover the full range of conditions that synthetic textiles encounter, and the criteria for what counts as “biodegradable” vary between national and international standards.14PubMed Central. Methodologies to Assess the Biodegradability of Bio-Based Polymers-Current Knowledge and Existing Gaps
This gap matters for consumers. When a product claims to be made from “biodegradable polyester,” the claim might be technically accurate under the specific test conditions used (high-temperature industrial composting, for instance) but misleading for what happens when the product ends up in a home compost bin, a landfill, or the ocean. Without harmonized standards that match real-world disposal conditions, the term “biodegradable” on a polyester product label does not tell you much about what will actually happen to it after you throw it away.
Practical Steps That Actually Help
Given that polyester will outlast you, your children, and possibly your grandchildren, the most effective approach is to keep it out of the waste stream and reduce the microfibers it sheds along the way. Washing polyester garments less frequently, at lower temperatures, and in front-loading machines all reduce microfiber release. Specialized laundry bags designed to capture microfibers can trap a meaningful fraction before they reach the drain. Buying fewer, higher-quality polyester garments that last longer reduces total waste, and donating or reselling clothing extends its useful life before it becomes waste at all.
For disposal, polyester textiles should ideally go to textile recycling programs rather than landfill, though the infrastructure for this varies enormously by location. Mechanical recycling of polyester into lower-grade products is already widespread for PET bottles, and enzymatic recycling of textile polyester is on the horizon. Composting polyester garments at home is pointless: they will sit in your compost pile unchanged while everything around them breaks down. If a garment contains a polyester-cotton blend, composting will only remove the cotton, leaving a loose mesh of polyester fibers scattered through your compost and, eventually, your garden soil.