What Is Polyester Fabric? The Full Spec Sheet, From a Mill
Polyester fabric is a synthetic cloth woven or knitted from filament or staple drawn out of PET polymer. This guide defines it by its measurable constants rather than by adjectives: melting and glass-transition temperature, moisture regain, filament fineness, the dyeing threshold and the weight band. Every number here is a value this mill uses daily.
10 sections 9 terms ~6 min
Most answers to “what is polyester fabric” are written by a retail blog rather than by a mill or a chemist: durable, wrinkle-resistant, quick-drying. None of that is wrong, but it is not enough to buy on, because none of it carries a measurable number. The definition below is built from the production side — from the values used every day by a plant that melts, draws, knits and dyes polyester.
What polyester is, defined by the fibre
In textiles, polyester means polyethylene terephthalate (PET) almost without exception. The polymer, made by polycondensation of PTA and MEG, is melted, pushed through spinneret holes into filaments and solidified in an air quench. That filament is either used continuous (filament yarn) or cut to length into staple fibre. Cloth then comes from weaving or knitting that yarn — so “polyester fabric” names a fibre, not a fabric construction. That distinction frames the rest of this page.
The spec sheet: polyester’s measurable constants
The table below gathers the values that govern how a polyester fabric behaves and that can be measured in a laboratory. Each row ties to a practical consequence: the ironing temperature, the dyeing recipe and the drying speed all follow from these constants.
| Property | Typical value | What it decides | How it is measured |
|---|---|---|---|
| Melting temperature (Tm) | ~255–260 °C | The ceiling for heat-setting and ironing; above it the fibre melts | DSC · ISO 11357 |
| Glass transition (Tg) | ~70–80 °C dry · ~65 °C in water | The threshold at which dye can enter the fibre | DSC · ISO 11357 |
| Moisture regain | 0.4% | Fast drying; dry and commercial weight are near-identical | Conditioned weighing |
| Intrinsic viscosity (IV) | ~0.62–0.66 dL/g (textile filament) | Chain length and tenacity | ASTM D4603 |
| Microfilament threshold | below 1.0 dpf | Soft hand, high opacity and moisture spreading | denier ÷ filament count |
| Dyeing temperature | ~130 °C (HT/HP) | Diffusion of disperse dye into amorphous regions | Dye recipe · pressurised vessel |
| Catalogue weight axis | 60–500 g/m² | The same fibre as tulle-thin and as jacket-lining firm | Product catalogue (42 fabrics) |
Polyester against cotton, viscose and wool: the difference in one number
Polyester’s two most discussed traits — drying fast and feeling sweaty — come from the same single number: moisture regain. Because the fibre holds almost no water it dries quickly when wet; but it cannot absorb and carry sweat, and moving that sweat to the surface is the job of construction and finish. The table sets the commercial regains side by side.
| Fibre | Commercial regain | Practical consequence |
|---|---|---|
| Polyester | 0.4% | Holds almost no water; the fastest drying and the most dimensionally stable |
| Nylon | 4.5% | Damper than polyester; stronger in abrasion |
| Cotton | 8.5% | Absorbs sweat but stays wet; slow to dry |
| Viscose | 12% | High absorbency, loses strength when wet |
| Wool | 16.5% | Holds moisture while generating heat; slowest to dry |
Woven or knitted: one fibre, two different cloths
Polyester can be woven and it can be knitted, and the two behave completely differently. Woven polyester (satin, poplin, chiffon, outdoor cloths) is built from warp and weft crossing at right angles: it stretches little, holds a pattern and frays at the edge. Knitted polyester (single jersey, interlock, piqué, mesh, fleece) is built from interlocking loops: it stretches, follows the body, and its cut edge either curls or does not ladder. A search result saying “polyester fabric” rarely says which is meant; in an order it is the first thing to settle. This mill produces the knitted side — we have no weaving programme.
Where polyester is genuinely strong
Dimensional stability: a heat-set polyester knit keeps its width and length through the wash cycle, which is pattern confidence for the garment maker. Colourfastness: disperse dye enters the fibre rather than sitting on it, so light and wash fastness run high. Abrasion and fatigue resistance: continuous filament does not break, and pilling is managed through structure and finish. Sublimation printing: the dye passes from a gas phase straight into the fibre, chemistry that cotton has no equivalent for — this is why digitally printed kit and promotional wear are polyester. And cost: building the same performance from natural fibre is usually more expensive.
Where it is weak — and how production compensates
Breathability is not polyester’s natural advantage; a densely knitted structure runs warm. The compensation is not to change the fibre but to change the STRUCTURE: perforated net, dotted mesh and channelled cross-sections carry air. Odour has less to do with the fibre than with bacteria on the surface; an antimicrobial finish is applied per order and reported by test. Static is a direct consequence of the low moisture regain; an antistatic finish or a blend reduces it. Microplastic shedding in the wash is a real issue, and it varies measurably with knit density, cut edge and finish. None of these say “polyester is bad”; each corresponds to a production decision.
Weight: “polyester fabric” is not a single mass
The same fibre can be a curtain-thin tulle at 60 g/m² and a jacket-lining double knit at 500 g/m². Our catalogue axis carries 42 fabrics between 60 and 500 g/m²; in an enquiry, “we want polyester fabric” is not a specification until it says where on that axis it sits. Once the weight is written next to the construction (jersey, interlock, piqué, mesh, fleece) and the elastane share, the request becomes measurable from the first sample.
Is recycled polyester (rPET) the same cloth?
As cloth, yes; as paperwork, no. rPET is the same polymer, obtained by flaking and re-melting post-consumer PET bottles; the same constructions are knitted on the same machines and the same hand and fastness are expected in practice. The difference is traceability: a recycled-content claim only means something under a chain-of-custody standard such as GRS, and is otherwise an unverifiable statement. The question to ask a supplier is not “is it rPET?” but “is it certified within GRS scope?”.
Care: why 40 °C and why a low iron
Care instructions are not arbitrary; they follow from the spec sheet. The glass transition sits around 70–80 °C dry and lower in water, so a gentle wash at 30–40 °C does not disturb the fibre, while high temperature relaxes the amorphous regions and can distort the garment. On the ironing side the ceiling is the melting temperature (~255–260 °C): the soleplate must stay far below it, typically on the 110 °C setting and with a press cloth. Chlorine bleach is neither needed nor advisable; polyester does not hold stains in the first place.
What to ask when buying
“Polyester fabric” is a starting point, not a specification. Five lines make a request measurable: the construction (woven or knitted, and which knit), the weight window in g/m², the composition and elastane share, the finish expected (wicking, water-repellent, antimicrobial, UV) and the certification (OEKO-TEX, GRS, the test reports you need). With those five lines two suppliers’ samples become comparable for the first time; without them the sampling round repeats, whichever name was used.
Frequently asked questions
What is polyester fabric?
Polyester fabric is a synthetic cloth woven or knitted from filament or staple drawn out of PET polymer. “Polyester” names a fibre, not a construction: the same fibre yields cloths as different as woven satin and knitted jersey. Its measurable spec sheet is a melting temperature of ~255–260 °C, a glass transition of ~70–80 °C and a moisture regain of 0.4%.
Does polyester fabric make you sweat?
The clammy feeling comes from the fibre’s 0.4% moisture regain: polyester does not absorb sweat. That is not inevitable, though — moving sweat to the surface is the job of structure and finish. Perforated net, dotted mesh and channelled fibre cross-sections carry air, while a wicking finish spreads moisture and speeds evaporation. A dense, heavy polyester runs warm; a light, porous structure does not.
At what temperature should polyester be washed?
At 30–40 °C on a gentle cycle. The limit is not arbitrary: polyester’s glass transition sits at ~70–80 °C dry and lower in water, and going above that threshold relaxes the amorphous regions and can distort the garment. On the ironing side the ceiling is the melting temperature (~255–260 °C), so the iron is used on its lowest setting (around 110 °C) and with a press cloth. Chlorine bleach is not needed.
Is polyester or cotton better?
It depends on the use, and the answer sits in one number: moisture regain is 0.4% for polyester and 8.5% for cotton. Cotton absorbs sweat but stays wet and dries slowly; polyester does not absorb but dries fast and holds its measurements after washing. For sportswear, team kit and promotional wear polyester wins — sublimation printing works on it alone — while for next-to-skin everyday items where absorbency is wanted, cotton or a blend is preferred.
Is polyester fabric bad for your health?
The cloth itself is an inert polymer and is not an allergen; certificates such as OEKO-TEX STANDARD 100 verify harmful-substance limits on the fabric. Two issues come up in practice: static and odour, both consequences of the low moisture regain and both managed by finish and structure; and microplastic shedding in the wash, which is a genuine environmental issue and varies measurably with knit density, cut edge and finish.
What weight does polyester fabric come in?
There is no single weight; with the fibre unchanged, the cloth can be tulle-thin at 60 g/m² and jacket-lining firm at 500 g/m². Our catalogue axis carries 42 fabrics across that range. In an order the weight alone is not enough: written next to the construction (jersey, interlock, piqué, mesh, fleece) and the elastane share, the request becomes measurable from the first sample.