Polyester, Nylon and Microfibre: How to Read a Synthetic Yarn Spec

Synthetic fabrics come with some of the most compressed specifications in textiles. A listing might say "75D/72F DTY polyester", "20D nylon ripstop" or "microfibre 150D/288F", and each part of that tells you something concrete about how the fabric will look, feel and wear. This guide decodes those specs for the three big synthetic families, polyester, nylon and acrylic, plus elastane, and shows how to convert their yarn figures with the site's yarn count converter. It also covers what makes a fabric "microfibre", and the practical differences that the spec does not spell out, such as heat, pilling and fibre shedding.

Filament and staple yarns

Synthetic fibres are extruded as continuous filaments. They can be used in two ways:

• Filament yarn: the continuous filaments are gathered into a yarn, sometimes with a little twist or texture. Smooth, strong and lustrous; the basis of most polyester and nylon fabrics for linings, sportswear, outdoor gear and hosiery.
• Staple (spun) yarn: the filaments are cut into short lengths, like cotton or wool fibres, and spun. Softer, fuzzier and more natural-looking; used for polyester-cotton blends, acrylic knitwear and fleece.

Filament yarns are usually described by denier or dtex and filament count. Spun yarns are described the way cotton or wool yarns are, by Ne or Nm, often with the fibre's own fineness quoted separately.

Decoding "75D/72F"

The first number is the total linear density of the yarn, here 75 denier: 9,000 metres of it weigh 75 g. The converter shows that as 8.33 tex or 83.33 dtex. The second number is how many filaments make up the yarn, here 72.

Dividing one by the other gives the fineness of each filament, the denier per filament or dpf. 75 ÷ 72 is about 1.04 dpf, or in dtex, 83.33 ÷ 72, about 1.16 dtex per filament. That single figure explains most of the difference in hand between synthetic fabrics of the same weight:

• 150D/48F: 3.47 dtex per filament. Firm and crisp, typical of a standard polyester.
• 75D/36F: 2.31 dtex per filament. Still fairly crisp.
• 75D/72F or 150D/144F: about 1.16 dtex per filament. Noticeably softer and more fluid.

Finer filaments mean more surface area for the same weight, which gives a softer handle, better drape, and more capacity to wick moisture along the yarn. They also mean each filament is weaker and easier to snag.

What makes a fabric "microfibre"

Microfibre is a name for fabrics made from very fine filaments. There is no single worldwide definition: the line is commonly drawn at about 1 dtex per filament, and some sources use 1 denier, which is slightly finer (1 denier is 1.11 dtex, and 1 dtex is 0.9 denier). Either way, it is the per-filament figure that counts, not the total yarn count. A heavy 300D yarn can be microfibre if it is made of hundreds of filaments; a light 20D yarn of 7 filaments is not.

Microfibres are used for cleaning cloths, where the fine filaments, often split during finishing, trap dust and grease; for peached and suede-like fabrics; for soft sportswear; and for bedding. A cleaning cloth made of split microfibre is a different product from a microfibre sheet, though both carry the name.

Textured, drawn and partially oriented yarns

Polyester and nylon filament specs often carry a three-letter code:

• FDY (fully drawn yarn): smooth and flat; used for woven linings, taffetas and many technical fabrics.
• DTY (draw textured yarn): crimped to give bulk and stretch; used in knits and in wovens that need a softer, more cotton-like hand.
• POY (partially oriented yarn): an intermediate product usually textured further before weaving.

Two fabrics with the same denier and filament count can feel very different if one is FDY and the other DTY.

Polyester, nylon, acrylic and elastane compared

Polyester

The most widely produced fibre in the world. Strong, resists stretching and wrinkling, absorbs very little water and dries fast, holds pleats when heat-set, and is cheap. It can feel clammy next to the skin and tends to hold body odour more than natural fibres. Used everywhere from shirts and linings to sportswear, fleece and technical fabrics.

Nylon (polyamide)

Stronger and more abrasion-resistant than polyester at the same weight, with more stretch and recovery. Absorbs a little more moisture. Used for hosiery, lightweight outdoor fabrics, swimwear and anything that must survive scuffing. Nylon is more sensitive to prolonged sunlight than polyester.

Acrylic

Almost always used as staple, often as a wool substitute in knitwear, blankets and outdoor furnishing fabrics. Warm, light and colourfast, but prone to pilling, and it can lose shape with heat. Solution-dyed acrylic, where colour is added before the fibre is formed, is widely used for awnings and outdoor cushions because it resists fading.

Elastane

Known by trade names such as Lycra and Spandex. Used in small proportions, often 2 to 10 percent, to give stretch and recovery. Elastane is weakened by chlorine and by high heat, which is why stretch fabrics need cooler washing and why swimwear wears out.

Reading denier in hosiery and outdoor fabrics

Two markets put denier on the label directly.

Tights and stockings are labelled with the yarn denier. 15 denier (1.67 tex) is sheer; 40 denier (4.44 tex) is semi-opaque; 70 to 100 denier is opaque. Knit structure changes the look as well, so two brands' 40 denier tights can differ.

Outdoor and bag fabrics are labelled with the yarn denier of the weave: 20D or 30D for ultralight shells and tent flies, 70D for general-purpose shells and linings, 210D and 420D for packs and tent floors, 600D and 1000D for heavy bags and luggage. A higher denier is heavier and more abrasion-resistant. The guide to choosing outdoor fabric covers those weights.

Heat, ironing and melting

Synthetic fibres are thermoplastic: they soften and melt with heat. That is useful in manufacturing, because it lets pleats be heat-set and edges be sealed with a hot knife, but it matters in use:

• Iron synthetics on a low setting, and press with a cloth. A hot iron can glaze or melt polyester and nylon in seconds.
• Do not tumble-dry elastane-rich fabrics hot.
• Synthetic garments can melt and stick to skin if they catch fire. People who work near open flames, sparks or molten metal wear flame-resistant clothing for that reason, and synthetic base layers are a poor choice around campfires and stoves. Where workwear has to protect against heat or flame, it must be certified to the relevant standard; ordinary synthetic fabric is not protective.

Pilling and fibre shedding

Staple synthetics, especially acrylic and polyester fleece, are prone to pilling because their strong fibres hold the pills on the surface rather than letting them break off. Filament fabrics pill less.

All synthetic textiles shed some fibre fragments in washing, and some of those fragments reach waterways as microplastics. How much a fabric sheds depends on its construction, finish and age, and research on the subject is still developing. Washing full loads at lower temperatures, using shorter cycles, and catching fibres with a filter or a washing bag designed for the purpose are commonly suggested ways to reduce shedding; how well each works varies between studies.

Comparing two synthetic fabrics

When comparing listings, line up:

1. Yarn linear density in one system. Convert denier to dtex, or the reverse, with the converter. 150D and 167 dtex are effectively the same yarn.
2. Filament count, and from it the dtex per filament.
3. Yarn type: FDY, DTY, or spun.
4. Fabric weight in GSM, converting from oz/yd² with the Fabric Weight Converter if needed.
5. Construction: weave or knit, and density.
6. Finishes and coatings, which can change weight and behaviour a lot.

What the converter does not tell you

The converter is exact for yarn linear density between denier, tex, dtex, Nm and Ne. It does not divide by the filament count for you, and it says nothing about fibre type, tenacity, texture or finishing. Those come from the supplier's specification. For performance claims, such as abrasion resistance, water repellency or flame resistance, look for test results to a named standard rather than a description.