Lyocell

Why a manufactured fiber is not a plastic here. Our plasticClass tracks what the polymer actually is, not how much industrial process it went through. In lyocell the polymer is cellulose, chemically unaltered - the FTC definition above says it explicitly, that no hydroxyl substitution and no chemical intermediates occur. Nothing petroleum-derived enters the backbone, the solvent (NMMO) is a processing aid rather than a component of the finished fiber, and the result biodegrades as cellulose. Polyester is the opposite case on every count. So lyocell rates as none, while remaining honest that it is manufactured, not picked. The contrast that matters is viscose, the older route to the same kind of fiber: viscose does substitute the hydroxyl groups and does form an intermediate, using caustic soda and carbon disulfide, and CS2 is a genuine occupational poison - peripheral neuropathy is the most consistent adverse effect documented in viscose rayon workers, and cardiovascular disease is the leading cause of increased mortality among them. None of that reaches the wearer of a finished viscose garment; it is a worker-and-emissions problem, and it is the honest reason to prefer lyocell. Modal sits with viscose, not with lyocell - it is a high-wet-modulus viscose made by the same CS2 chemistry, and it is not even a separate generic fiber name under FTC rules. Bamboo fabric is the same story with better marketing: the FTC's position is that most bamboo textiles are rayon, that there is no trace of the original plant in the finished fiber, and that only mechanically processed bamboo may be called bamboo at all - a position it has enforced with penalties against major retailers. Against skin the finished fiber is inert cellulose in every one of these cases.

Cellulose, so it burns rather than melting and has nothing to migrate when warm. The practical heat limit is dimensional: lyocell is washed cool and dried gently, and a hot dryer is what shrinks it and what degrades any elastane blended in with it.

Lyocell is smooth, cool, notably heavier in drape than cotton of the same weight, and has an even, almost silky surface with none of cotton's fuzz. The label is where the real distinctions live, and they are legal rather than aesthetic. Anything sold as bamboo fabric, bamboo viscose or bamboo rayon is regenerated cellulose, not bamboo fiber - the plant is only the pulp source. Rayon or viscose on a label means the CS2 route; modal means the same chemistry with more stretching; lyocell or TENCEL means the NMMO route. If a brand says only eco fabric, plant-based or wood-based, ask which of those four words is on the care label. And check for elastane, which is added to lyocell knits for stretch as routinely as it is to cotton.

Lyocell fibrillates: under wet mechanical abrasion, fine fibrils detach along the fiber and give a hairy surface that reads as frosting on dyed fabric. Manufacturers control this in finishing with acid catalysts and crosslinkers, but it is why lyocell is markedly more abrasion-sensitive when wet than cotton, which has an inherently very low fibrillation tendency. Wash cool and gentle, skip the hot dryer, and expect a lyocell garment to keep its drape but slowly lose crispness.

Lyocell biodegrades as cellulose, and this is one of the few textile claims with clean independent testing behind it: in coastal seawater, lyocell along with cotton, modal and viscose disappeared completely in about 35 days and reached 76 to 82 percent biodegradation in a 28-day bioreactor, while PLA showed 0.2 percent and PET and PP showed no visible breakdown past 231 days. Lenzing's standard lyocell also carries TUV Austria certification as biodegradable in soil, freshwater and marine environments. The catch is blends: in a cellulose-synthetic blend only the cellulose goes, and what is left is a thinning plastic skeleton in the original shape of the garment. A lyocell-elastane knit is not a biodegradable garment.