Wool

Wool is keratin protein — the same stuff as hair — and the most technical natural fiber you can buy: it insulates when wet, resists odor for days, regulates temperature, and is naturally flame-resistant.

It biodegrades fully, and shed wool fibers are nutrients, not pollution. One caveat: superwash-treated wool carries a thin polymer coating for machine-washability; untreated or GOTS-certified wool avoids it.

Wool, merino, cashmere, and other animal fibers score 0/100. A “50% wool, 50% acrylic” sweater scores 50 — the acrylic half.

The same weight applies everywhere: a product's score is the percentage-weighted plastic share of its listed fiber composition, and every weight is public.