Wool

Wool is keratin, the same protein family as hair and fingernails, with about 2-3% residual lipid. There is nothing in the fiber to leach into skin, food or air. The catch on this site is not toxicity but composition. Roughly 70% of wool sold as fully machine washable has been through the chlorine-Hercosett process: chlorine strips the fiber's outer 18-MEA lipid layer and etches its scales, then a polyamide-epichlorohydrin resin (Hercosett 125) is applied at 1-2% on weight of fiber so the scales can no longer interlock. One manufacturer that uses the process describes the resin plainly as a "nylon-based polymer." That is a thin, permanently bonded synthetic film on an otherwise natural fiber - not a leaching hazard, but the reason a superwash wool garment is not honestly plastic-free. The chlorination step also puts AOX into the effluent, which is why the process is restricted in a number of developed countries.

Wool does not melt or drip. It ignites at a higher temperature than cotton and most synthetics, spreads flame slowly and chars instead of forming a molten bead, which is why it survives in blankets and upholstery where polyester is a liability. The heat risk with wool is dimensional rather than chemical: hot water plus agitation felts it, and shrinkage of 25-30% is normal for untreated wool put through a hot machine wash. Dryer balls are the exception that proves the point - they are already fully felted, so a hot dryer does nothing further to them.

Burn a single fiber pulled from a seam. Wool smolders, smells like burning hair, self-extinguishes and leaves a black ash you can crush between your fingers; acrylic and polyester shrink from the flame, melt into a hard bead and smell chemical. On a dryer ball, density is the tell - a real one is felt all the way through and stays heavy; cut a suspicious one open and look for a synthetic yarn or foam core under a thin wool wrap. On garments, "superwash", "machine washable", "total easy care" and a machine-wash symbol on a wool label all point to the resin treatment above unless the brand says otherwise. If a spec sheet says only "wool", ask two things: is it superwash or chlorine-Hercosett treated, and what is the full fiber breakdown including any nylon or elastane.

Clothes moth larvae eat keratin, and their documented targets include wool clothing, carpets, rugs, upholstery and the animal bristles in brushes. They are drawn to soiled fiber, so store wool clean and sealed; cedar oil kills only small larvae and loses potency after a few years, so the airtight container matters more than the wood. Otherwise wool asks very little: air it out rather than washing it, wash cool without agitation, dry flat. Dryer balls run hundreds of loads before they pill down to nothing.

Untreated wool decomposes in soil over months to a few years, releasing nitrogen as it goes, and will break down on a home compost heap if cut up. Superwash wool carries a resin that does not biodegrade, and any blend with nylon or elastane will not compost and sheds synthetic microfiber for as long as it exists. No curbside program takes wool. Textile take-back and mechanical "shoddy" recycling into felt and insulation are the real routes, and both want clean, unblended fiber.