Which Fabrics Are Biodegradable, and How Do They Wash?

Fabrics made from natural fibres, and from cellulose regenerated from wood pulp, are generally biodegradable: given the right conditions, microorganisms break them down. That is a real advantage at the end of a textile's life. It comes with a trade-off during its life, though. The same fibres that biodegrade also tend to absorb water, swell, shrink and lose strength when wet, so they need more care in washing than synthetics. This guide sets out which fabrics biodegrade and what gets in the way, then covers how those fabrics behave in the wash, with worked shrinkage figures from the site's Fabric Shrinkage Calculator.

Which fibres biodegrade

• Plant fibres: cotton, linen (from flax), hemp, jute, ramie. Made of cellulose, which soil microorganisms readily break down.
• Animal fibres: wool, silk, alpaca, cashmere. Made of protein, which also biodegrades, though wool's rate depends a lot on conditions.
• Regenerated cellulose: viscose (rayon), modal, lyocell, cupro. Wood pulp or other plant cellulose is dissolved and spun into new fibre. Chemically still cellulose, so generally biodegradable.
• Bio-based synthetics such as PLA: compostable under industrial conditions, but slow in soil, home compost or water. The guide to PLA and bio-based fibres sorts out those claims.
• Conventional synthetics: polyester, nylon, acrylic, elastane. Not meaningfully biodegradable in normal environments.

What gets in the way

A garment is more than its main fibre. Several things can stop a "natural" fabric from breaking down as you might expect:

• Blends. A cotton-polyester shirt leaves the polyester behind. Even a few percent of elastane in a stretch cotton is a synthetic component.
• Thread and trims. Most sewing thread is polyester or polyester-cored. Labels, interfacings, zips, buttons and elastic are often synthetic.
• Finishes and coatings. Water-repellent, wrinkle-resistant, flame-retardant and other finishes, and coatings such as PU, change how a fabric breaks down and may leave residues.
• Dyes. Most dyes do not prevent biodegradation, but some dyes and printing pastes contain substances you would not want in compost.
• Conditions. Biodegradation needs moisture, oxygen, warmth and microbes. A cotton T-shirt in a dry, compacted landfill can last a very long time.

So "biodegradable fabric" is best read as "made of a fibre that can biodegrade in suitable conditions". Whether a whole garment does so, and whether it is a good idea to put it in compost, depends on everything else in it and on your local waste guidance. Many councils and waste services advise against putting textiles in garden or food compost at all, and offer textile collection for reuse and recycling instead.

Why the same fibres shrink

Cellulose and protein fibres absorb water. When they do, they swell, and a woven or knitted fabric whose yarns have been stretched in manufacturing relaxes and contracts. This relaxation shrinkage happens mostly in the first few washes. Wool can also felt: its fibre scales lock together under heat, moisture and agitation, and the fabric shrinks and thickens permanently.

Synthetic fibres absorb very little water and have usually been heat-set, so they shrink much less in normal washing. That is one reason synthetic blends are popular: they reduce shrinkage and creasing, at the cost of end-of-life breakdown.

How much? Test, do not guess

Shrinkage varies widely with construction and finishing, so figures for a fibre type are only rough guides. The reliable approach is a wash test: mark a measured length on a sample, wash and dry it as the finished item will be, and measure again. Illustrative results:

• a linen sample marked at 100 cm that comes back at 92 cm has shrunk 8%;
• a viscose sample marked at 50 cm that comes back at 46 cm has also shrunk 8%;
• a pre-shrunk cotton marked at 100 cm that comes back at 97 cm has shrunk 3%.

These are examples of how to read results, not typical values for those fibres. Test your own fabric in both directions; the full method is in the guide to measuring shrinkage with a wash test.

Once you have a figure, the calculator's pre-cut mode tells you how much to allow. For a 3 m finished length in a fabric that shrinks 8%, cut or buy 3.26 m. At 4% it would be 3.13 m.

Washing guide by fibre

Cotton

Robust when wet. Can usually be machine-washed warm, but expect some shrinkage on the first washes unless pre-shrunk. Tumble drying increases shrinkage and wear.

Linen and hemp

Strong, and stronger wet than dry, but prone to shrinkage and creasing. Softens with each wash. Avoid over-drying, which makes linen brittle at the folds; iron while slightly damp.

Viscose, modal and rayon

Weaker when wet, sometimes much weaker. Wash gently, do not wring, and dry flat or on a hanger. Can shrink noticeably and lose shape if washed hot or tumble-dried. Modal and lyocell are generally more robust than standard viscose.

Lyocell

Stronger wet than viscose. Some lyocell fabrics can fibrillate, forming a fine fuzz on the surface, if abraded while wet; gentle cycles and washing inside out help.

Wool

Wash cool and gently, or by hand, with a wool detergent, unless the label says it is treated to be machine-washable. Never put untreated wool in a hot wash or a hot dryer; it can felt irreversibly. Dry flat.

Silk

Many silks can be hand-washed in cool water with a mild detergent, but some dye and finish combinations cannot; follow the label, and test an inconspicuous area.

Making biodegradable fabrics last

From an environmental point of view, how long a garment is worn usually matters more than whether it can biodegrade at the end. Washing natural fibres cooler and less often, drying them on a line, mending small holes, and storing wool away from moths all extend a textile's useful life. When it is worn out, reuse and recycling routes generally keep more value than disposal.

Sewing with natural fibres and planning for shrinkage

If you are making something from a natural-fibre fabric, pre-wash it the way you will wash the finished item, or cut larger by the measured shrinkage. The guide to pre-washing fabric covers the choice. For buying, use the Fabric Yardage Calculator for the length you need, and the shrinkage calculator for the extra.

If you want a garment that can biodegrade as completely as possible, choose a single natural fibre, cotton or linen thread, and natural-material trims, and avoid synthetic finishes. Labels such as organic or other fibre certifications tell you about how the fibre was grown or processed, not necessarily about the thread and trims.

What the calculator covers

The shrinkage calculator turns your before-and-after measurements into a percentage, and a percentage into a pre-cut length. It cannot tell you how much a fabric will shrink before you test it, and it says nothing about how or whether a fabric will biodegrade. For end-of-life questions, follow your local waste and textile-collection guidance.