Fibres · Synthetic
PLA (polylactic acid / bioplastic)
The plastic that grows from plants: a polyester made from the sugars of maize, cane or beet instead of petroleum. Lustrous, light and stable, but not very elastic and sensitive to heat, it calls for a careful hand in washing and ironing.
Translated from Italian. A native knitter has not reviewed this translation yet.
History
It was born as a plant-based alternative to fossil polyesters: instead of crude oil, the raw material is the sugar of farm crops, fermented into lactic acid and then polymerised. Industrial-scale production began in the early 2000s and remains concentrated in a few large chemical hubs, in the United States, Thailand and Europe. In knitwear it arrives mostly as a component of blends, where it brings lustre and green credentials without the environmental weight of traditional synthetics.
How the yarn is made
Plant sugars are fermented into lactic acid, which is condensed into a molten polymer; this is extruded through spinnerets into continuous filaments and then drawn to orient the molecules and give tenacity. The yarn can stay shiny and compact as a filament, or be cut into staple and spun with other fibres for a warmer, more matt hand. There is no shearing or combing: everything depends on extrusion and drawing.
Why it is prized
It is the simplest way to give a knit lustre and coolness without resorting to petroleum: a renewable origin, good strength and a smooth, dry touch. In blends it lightens the garment, adds brilliance and stabilises the shape, while remaining a more sustainable choice than classic polyester.
Dyeing
It is dyed with disperse dyes, like other polyesters, but at lower temperatures because heat softens it: this somewhat limits the range of deep dark shades and calls for controlled baths. Done well, the result is clean and bright, with good lightfastness.
Care
Handle it gently: wash in cold or lukewarm water, never hot, with a light spin. It dislikes heat, so avoid the tumble dryer and a hot iron, or use them at the lowest setting with a pressing cloth. On the other hand it does not felt, forms no halo and has little tendency to pill, so the garment stays crisp and defined over time.
End of life
It is compostable in industrial facilities, where controlled heat and moisture break it down into lactic acid and then into water and carbon dioxide; in home compost or landfill, however, it stays stable for a long time. In blended garments separating it from the other fibres is difficult, so the environmental benefit is fully realised only in single-fibre items and in the right composting stream.
How to recognise it
| Hand | Smooth, dry and slightly cool to the touch, with a silky slip. It lacks the warm springiness of animal fibres: the knit feels stiffer and less bouncy. |
|---|---|
| Look | Lustrous and even, with no natural crimp: the surface is regular and reflects light like a fine polyester, but with a slightly more subdued, glassy tone. |
| Behaviour | It drapes fluidly and coolly, recovers only modestly after stretching and tends to take creases if heated. It breathes better than classic polyester and dries quickly. |
| Burn test | A synthetic signature, but a peculiar one: it melts and shrinks away from the flame, burns with drips and a sweetish, almost caramel smell, different from the chemical smell of polyester, and leaves a hard, pale residue. |
| Home tests | Burn test: melts and drips, sweet caramel smell, hard residue · Heat test: a warm iron softens it and makes it shiny at once, a sign of its heat sensitivity · Stretch test: pull and release, it only partly recovers, with no bounce |
| Confused with | Polyester, almost identical in appearance: but PLA melts at a lower temperature and burns with a sweet, not chemical, smell · Bright viscose, similar in brilliance: but viscose burns like paper in the flame, without melting |
| Only in a lab | Telling PLA from other polyesters with certainty and confirming its plant origin requires laboratory analysis, by spectroscopic identification of the polymer (FTIR) or determination of biobased carbon. |
Physical facts
| Property | Value | Source |
|---|---|---|
| elastic memory | Low | research |
| sag | Medium | research |
| halo | None | research |
| felting risk | None | research |
| fineness (µm) | — | research |
| moisture regain (%) | 0.5 | research |
| typical shrinkage (%) | 0–10 | estimate |
| staple length (mm) | — | research |
measured = a measurement with a reference · iso = a standard · research = a verified source · estimate = plausibility only
Good for
lustrous, light garments · blends that need brilliance · breathable summer knitwear · cool, dry-handed effects
Less good for
ribs and cuffs that must bounce back · garments that need hot ironing · heavy, structured knitwear that must hold its shape