How polyester and viscose fabrics are made
Polyester reaches the weaver as continuous filament yarn, either partially oriented (POY) and then textured (DTY), or fully drawn (FDY), or as spun yarn made from cut staple fibre. Viscose, a regenerated cellulose fibre, is mostly used as spun yarn, often blended with polyester. Fabrics are woven on water-jet, air-jet or rapier looms, or knitted.
Processing is where the two fibres part ways. Polyester is dyed with disperse dyes at high temperature in jet machines, then heat-set on a stenter, which fixes its width and makes it dimensionally stable. Viscose takes reactive dyes, like cotton, is weak when wet and shrinks readily unless it is properly relaxed and finished. Blended PV fabric needs two dye classes, one for each fibre, and the shade must match on both.
The Surat Municipal Corporation says Surat produces about 40% of India's man-made fabric; it gives no date for the figure. Surat's weaving, processing and printing units supply both export orders and India's own saree and dress-material trade. Surat is a Town of Export Excellence for gems and jewellery, not for textiles.
What we check on polyester and viscose fabrics
| Check | How it is checked | What fails |
|---|---|---|
| GSM | Circular cutter swatches from sampled rolls weighed on a balance | Weight below tolerance, which is common when a lighter yarn denier is substituted |
| Width | Usable width measured at several points along each roll | Narrower than ordered; width varying after uneven heat-setting |
| Shade | Swatches compared with the standard in a light box; the mill's spectrophotometer readings reviewed against the agreed CMC tolerance | Visible difference, or a colour difference above the agreed CMC value |
| Bow and skew | Weft line measured against a straight edge across the width | Over the limit; stripes and prints off-square |
| Barré and streaks | Fabric viewed at a low angle on the frame for repeating bands | Bands across or along the fabric from mixed yarn lots |
| Fault grading | 4-point system on a lit frame | Points per 100 square yards over the limit |
| Hand and finish | Feel, drape and surface compared with the approved sample | Harsh, papery or over-softened fabric; shiny press marks |
| Lab samples | Swatches sealed for fibre blend, pilling, dimensional change and colour fastness | Results outside the specification |
Blend ratio and pilling grade cannot be judged by eye or touch. They come only from an accredited lab on sealed samples.
Common defects by fibre
| Defect | Typical cause | Class |
|---|---|---|
| Fibre blend not as declared | More polyester and less viscose than the label says, or "bamboo" viscose sold as bamboo | Critical |
| Barré in polyester | Filament yarn from different production lots (merge numbers) woven together; they take dye differently | Major |
| Shade difference between rolls or batches | Batch-to-batch dyeing variation; second dye class off in PV blends | Major |
| High shrinkage in viscose | Fabric not relaxed before finishing | Major (from lab result) |
| Pilling | Spun polyester's strong fibres hold pills on the surface instead of shedding them | Major (from lab result) |
| Filament breaks and snags | Damaged guides or rough handling of smooth filament fabric | Major or minor by size |
| Oligomer or dye spots | Deposits from high-temperature polyester dyeing | Minor to major by visibility |
| Crush marks on viscose | Wet fabric creased in processing | Minor |
Market rules for synthetic fabrics
- Bamboo and rayon (US). The FTC says textiles made from bamboo-derived viscose must be described as rayon, or "rayon made from bamboo", not as bamboo. A fabric sold to US brands as "bamboo" is a labelling risk that starts on the mill's roll ticket.
- Fibre names (EU and Canada). Products made from the fabric need fibre composition in harmonised names, such as viscose and polyester, with percentages. See EU textile labelling and Canada textile labelling.
- Restricted substances. Disperse dyes include some that brands restrict, and azo dyes releasing listed amines are banned in EU textiles that touch the skin. See azo dyes and restricted substances.
- Flammability (US). Light, sheer synthetic fabrics for clothing must meet 16 CFR 1610. See 16 CFR 1610.
Packing, transit and your purchase order
Smooth filament fabrics slide off their tubes and crease if rolls are loose, and satin and georgette mark easily. Rolls should be tightly wound on firm tubes, wrapped in polythene and laid flat. Viscose is heavy for its volume and absorbs moisture, so wet or warm storage can leave water marks. Each roll ticket should show the shade lot, so rolls from one lot can be cut together.
Put these in your purchase order:
- Fibre content with tolerance, yarn type (filament or spun) and denier or count.
- GSM, width and construction, with tolerances.
- Shade standard, light source and CMC tolerance; number of shade lots allowed.
- Bow and skew limit and fault limit in points per 100 square yards.
- Pilling grade, dimensional change and fastness grades, with test methods.
- Restricted substances list and any certificate required.
- Roll length, packing and ticket content; no "bamboo" wording on viscose for the US.
The same Surat fabric is often bought as finished goods: see synthetic and printed sarees and dress materials and embroidered fabrics. Book an inspection in Surat or anywhere in India.
Sources
- Surat Municipal Corporation: The City, Contribution (undated)
- DGFT: Appendix 1B, Towns of Export Excellence (Surat: gems and jewellery)
- FTC: How to avoid bamboozling your customers
- Regulation (EU) No 1007/2011 on textile fibre names (EUR-Lex)
- ASTM D5430: Standard test methods for visually inspecting and grading fabrics