School-uniform trouser fabric selection
A school-uniform supplier must choose between two trouser fabrics for a 1,200-pair order. Fabric A is 100% cotton 3/1 twill, 240 g/m², 28 tex warp/30 tex weft, Martindale 25,000 cycles, warp shrinkage 3.5%, weft 1.8%, pilling grade 3–4, $4.20/m at 150 cm. Fabric B is 65% polyester/35% cotton twill, 220 g/m², 20 tex/2 warp, 24 tex weft, Martindale 40,000 cycles, shrinkage 0.8%/0.6%, pilling grade 2–3, $3.60/m. The school washes at 60°C and tumble-dries. Pupils say current cotton trousers fade and shrink; parents say polyester feels clammy. The marker uses 1.65 m per pair. The supplier must guarantee colour retention for 40 washes and no more than 2% shrinkage. A 30-pair trial is possible. Recommend a fabric, with conditions, and explain the fibre, yarn and weave trade-offs.
1. Compare both fabrics against the school's requirements. Which would you select, and what conditions would you attach?
Read the worked answer
Decision: Select Fabric B only if pilling can be controlled; otherwise Fabric A needs a pre-shrunk, colourfast finish.
Requirement check: Shrinkage: A's warp 3.5% fails the 2% limit; B's 0.8%/0.6% passes. Abrasion: both exceed a normal school-trouser target of about 20,000 cycles, but B is stronger (40,000 vs 25,000). Cost: A costs 1.65 × $4.20 = $6.93 per pair; B costs 1.65 × $3.60 = $5.94, a saving of $0.99 × 1,200 = $1,188. Colour retention over 40 washes favours the polyester blend, but pilling grade 2–3 is a warning; polyester/cotton staple blends can pill where abrasion releases fibres.
Judgement: B meets shrinkage, durability and cost, but pilling and clamminess are real risks. Conditions: specify compact-spun or longer-staple yarn, a pilling-resistant finish, and verify grade 3–4 after 40 washes; trial 30 pairs with the school's wash regime. If the trial fails pilling, use A with compressive shrinkage and a tested colourfast dye, accepting higher cost.
Why not simply choose A? A's comfort and appearance suit parents, but 3.5% warp shrinkage would break the guarantee after repeated 60°C washes.
2. Explain how the fibre, yarn and weave differences affect abrasion resistance, shrinkage and comfort.
Read the worked answer
Fibre: Cotton absorbs moisture and feels cooler, but at 60°C it relaxes and can shrink; polyester is hydrophobic, strong and colour-retentive, yet traps heat and feels clammy unless the fabric is open or moisture-wicking. The 65/35 blend balances these, explaining B's lower shrinkage and better colour retention.
Yarn: B's 20 tex/2 plied warp uses finer, folded yarns; plied yarns resist abrasion and withstand loom and laundry tension better than A's single 28 tex warp. Finer weft yarns give a smoother surface but can pill if short fibres work loose. A's coarser single yarns give a more rugged hand but shrink more because of greater yarn crimp and water swelling.
Weave: Both are 3/1 twills, so long floats expose more fibre to rubbing than a plain weave, improving drape but increasing pilling risk. The twill direction and sett affect air permeability: a tighter sett improves abrasion resistance but reduces comfort. B's lower mass (220 vs 240 g/m²) may feel lighter, but its synthetic content needs a finish or open sett to avoid clamminess. The trial must test pilling and wear, not just lab abrasion.
3. Outline the 30-pair trial and the acceptance criteria you would use before placing the bulk order.
Read the worked answer
Trial design: Make 30 pairs in the proposed B fabric using the production marker, thread and seam types. Record fabric batch, shade and finish. Wash 10 pairs for 40 cycles at 60°C with the school's detergent and tumble-dry; wash another 10 for 10 cycles; keep 10 as controls. Measure shrinkage before and after on a marked 50 cm square, and assess pilling, colour change, seam slippage and abrasion at cuffs, knees and seat.
Acceptance criteria: Mean shrinkage no more than 2% in either direction, with no single pair above 2.5%; pilling grade at least 3–4 after 40 washes; colour change no worse than grade 4 on the grey scale; no seam failure or obvious clamminess complaint in wear. Cost must remain at or below $5.94 per pair.
Decision rule: If B fails pilling, do not simply accept it because it is cheaper; cost the A option with pre-shrinking and a colourfast finish. If both fail, specify a third fabric rather than weakening the guarantee.