What is biodegradable sewing thread?

Biodegradable sewing thread is thread made from natural or plant-based fibre that breaks down after disposal, rather than persisting in landfill the way standard polyester thread does. It's a small detail most brands don't think about, because it's invisible once a garment is finished. But it's the difference between a garment that fully returns to the earth and one that leaves synthetic fibre behind long after the fabric itself has gone.

Why this matters more than it looks like it does

A garment can be made from natural, biodegradable fabric and still leave a synthetic footprint, because the thread holding every seam together is almost always polyester. Polyester thread doesn't break down. It doesn't matter how sustainable the fabric is if the stitching holding it together lasts centuries longer than the garment does.

What I use instead

I sew with Tencel lyocell thread, the same thread I use across my garments. It's Cradle to Cradle Gold certified and Oeko-Tex Standard 100 certified, both at the thread level. Made from wood pulp cellulose, it breaks down naturally rather than sitting in landfill indefinitely, unlike standard polyester thread. It costs more than standard thread, is harder to source and its an element of making clothes that isn't questioned by consumers, so most brands don't use it. I use it anyway, because a garment made to be worn for years and passed on shouldn't be held together with something designed to outlast it by decades.

The bigger picture

This is one small decision, applied consistently. It sits alongside cutting from pre-consumer waste denim and making most pieces to order rather than to a forecast. None of these choices are dramatic on their own. Together, they're the difference between clothing that's built to be replaced and clothing that's built to be kept.