Fibres · Synthetic
Polypropylene (Polycolon)
The lightest fibre there is, so light it floats on water: it absorbs no moisture, pushes it away from the skin and dries in no time. It is the technical choice for sport and next-to-skin layers, not for the cosy warmth of lounging.
Translated from Italian. A native knitter has not reviewed this translation yet.
History
It was born in 1954 from the work of Giulio Natta at the Politecnico di Milano, who synthesised isotactic polypropylene: research that earned him the Nobel Prize in Chemistry in 1963. A whole family of materials grew out of that discovery; in knitwear the fibre established itself above all in technical underwear and thermal base layers, where the trade name Polycolon became almost a synonym for dope-dyed yarn for sport.
How the yarn is made
It is produced by extrusion: the molten polymer is forced through spinnerets and drawn into a continuous filament, then possibly textured to give it bulk and stretch. Colour is almost always added in the mass, by mixing pigment into the melt before spinning, so the shade is part of the fibre rather than a layer deposited on the surface.
Why it is prized
Its merit is technical, not noble: it is the lightest textile of all and the only one that in practice does not get wet. Holding no water, it keeps the skin dry and moves sweat towards the outer layers, where it evaporates. In knitwear it gives extremely light garments that dry fast and stay warm when wet, ideal as a base layer under a wool sweater.
Dyeing
It is a difficult fibre to dye in a bath, because it has no chemical sites for common dyes to bind to and absorbs no water. This is why it is almost always dope-dyed, with pigments dispersed in the molten polymer: the result is excellent colourfastness to washing and light, but a range of shades fixed at spinning rather than free in the dyehouse.
Care
Very easy to wash and very quick to dry, it does not felt or shrink in water. Its real limit is heat: it melts at a low temperature, so no hot iron and no harsh tumble drying. It tends to hold body odours more than other fibres, so it likes frequent washing at low temperature.
End of life
It is not biodegradable: it is a petrochemical polymer that persists in the environment for a long time. On the other hand it is technically recyclable, being a single, thermoplastic material: melted and re-extruded it becomes yarn or product again, provided the garment is not blended with other fibres that are hard to separate.
How to recognise it
| Hand | Surprisingly light in the hand, almost waxy and dry to the touch, lukewarm but without the lively warmth of wool. The yarn runs smoothly and has a faintly plastic feel. |
|---|---|
| Look | From matt to slightly waxy, with no real silky lustre and no natural crimp; bulk, when present, comes from industrial texturing of the filament, not from crimp in the fibre. |
| Behaviour | Medium elasticity and fair recovery, a light and somewhat stiff drape. It absorbs no water, so it stays warm even when wet and dries very fast; it tends to build up static and attract dust. |
| Burn test | Clean synthetic signature: it melts and drips before burning, clear flame with a blue base and yellow tip, smell of paraffin or wax, residue in a hard bead of melted plastic. |
| Home tests | Float test: a tuft placed in water stays afloat, because it is lighter than water · Burn test: melts and drips into a hard bead, smells of wax and not of burning hair · Drop test: water beads on the surface and is not absorbed |
| Confused with | Polyester: very similar to the touch and in the flame, but polyester absorbs a trace of moisture, sinks in water and burns with a sweeter smell · Polyethylene: another light polyolefin, only certainly distinguishable in a laboratory |
| Only in a lab | Telling it reliably from other polyolefins and from polyester requires laboratory analysis: density in a gradient column, melting point and infrared spectroscopy (FTIR), as well as ISO 1833 selective dissolution. |
Physical facts
| Property | Value | Source |
|---|---|---|
| elastic memory | Medium | research |
| sag | Low (extremely light fibre) | research |
| halo | None | research |
| felting risk | None | research |
| fineness (µm) | — | research |
| moisture regain (%) | 0.0 | research |
| typical shrinkage (%) | 0–5 | estimate |
| staple length (mm) | — | research |
measured = a measurement with a reference · iso = a standard · research = a verified source · estimate = plausibility only
Good for
technical base layers and thermal underwear · sportswear that must dry quickly · trekking and activity socks · next-to-skin layers under wool
Less good for
lounge and warm knitwear (poor breathability at rest) · garments that need a hot iron · soft, heavy drape · garments designed for maximum comfort at rest