Fabric Construction
Fabric Construction asks you to identify how a fabric was built and to express its build numerically: ends and picks, cover factor, crimp and GSM. These numbers are the language of fabric specification sheets.
Construction routes
- Woven: two sets of yarns (warp and weft) interlaced at right angles; selvedges run along the warp.
- Knitted: loops intermeshed; stretchy and porous.
- Nonwoven: a web bonded by needle punching, spunlacing, thermal or chemical bonding; no yarn stage.
- Braided and lace structures sit outside the three main routes.
The counting rules
- EPI = ends per inch along the warp; PPI = picks per inch along the weft. Never swap them.
- Pierce cover factor for warp: K = EPI / square root of Ne.
- Crimp % = (yarn length minus fabric length) / fabric length x 100. In plain weave, warp crimp usually exceeds weft crimp because the warp is under tension during weaving.
- GSM = mass in grams per square metre.
Worked example
A 100 cm2 GSM cutter gives a conditioned swatch weighing 2.35 g. Find the GSM. Area = 100 cm2 = 0.01 m2. GSM = 2.35 / 0.01 = 235 g/m2. Now check cover factor for the same fabric: 40s Ne warp at 100 EPI gives K = 100 / square root of 40 = 100 / 6.32 = 15.8, a normal poplin-level cover.
Traps that cost marks
- Reporting EPI as PPI, or counting both systems as one figure.
- Using the GSM cutter on a thick, uneven or wrinkled sample, which inflates mass.
- Forgetting to condition samples before weighing.
- Treating higher GSM as automatically better quality; a 235 g/m2 canvas and a 235 g/m2 flannel behave completely differently.
- Writing crimp as a ratio rather than a percentage.