Construction analysis breaks a woven fabric down into its basic specification: threads per inch, yarn counts, weave, crimp and weight. Merchandisers use it to develop or re-source a fabric from a sample; quality teams use it to check bulk against the specification.
Writing a construction#
A woven construction is usually written as:
Warp count x Weft count / EPI x PPI, width, weave
Example: 40 x 40 / 133 x 72, 58 inch, plain weave. This means 40s Ne warp and weft, 133 ends per inch, 72 picks per inch, 58 inches wide.
Step 1: Condition the sample#
Leave the fabric in a standard atmosphere, as the test method describes, before measuring. Moisture changes yarn dimensions and weight.
Step 2: Count EPI and PPI#
- EPI (ends per inch): warp yarns per inch, counted across the width.
- PPI (picks per inch): weft yarns per inch, counted along the length.
Use a pick glass (counting glass) or a digital microscope. Count over at least 1 inch in several places, away from the selvedge. For dense fabrics, count over a smaller distance and multiply. Methods such as ISO 7211-2 and ASTM D3775 describe the procedure.
Step 3: Identify the weave#
Look at the interlacing pattern: plain (over one, under one), twill (diagonal lines), satin (long floats) or other. Note the direction of twill lines.
Step 4: Measure crimp#
Crimp is the waviness of yarn in the fabric. Mark a length on the fabric, remove a yarn, straighten it under a small tension, and measure its length.
Example: a warp yarn from a 10.0 cm length measures 10.8 cm when straightened. Crimp = (10.8 - 10.0) / 10.0 × 100 = 8%.
Step 5: Find the yarn count#
Remove a known number of yarns of known straightened length, weigh them on a precise balance, and calculate the count.
Example: 50 warp yarns, each 20 cm straightened (total 10 m), weigh 0.148 g. Tex = 0.148 / 10 × 1000 = 14.8 tex, which is about 40 Ne (590.5 / 14.8 = 39.9).
Use the yarn count converter for other systems. Note that yarn taken from finished fabric may differ from the original yarn because of dyeing and finishing.
Step 6: Measure GSM#
Cut and weigh a sample of known area. See fabric GSM.
Step 7: Check against a calculated GSM#
You can estimate GSM from the construction:
where and are warp and weft crimp as fractions, and and are the counts in tex.
For the example fabric, with 14.8 tex in both directions, 8% warp crimp and 5% weft crimp:
- Warp: 133 × 1.08 × 14.8 = 2,125.9
- Weft: 72 × 1.05 × 14.8 = 1,118.9
- GSM ≈ (2,125.9 + 1,118.9) / 25.4 = 127.7
The fabric GSM calculator woven method does this for any count system. If the calculated and measured GSM are far apart, recheck the counts and crimp; finishing add-on and shrinkage also explain some difference.
Checklist#
- Sample conditioned
- EPI and PPI counted in several places
- Weave identified
- Warp and weft crimp measured
- Warp and weft counts calculated
- GSM measured and compared with calculation
- Construction written in standard form
For strength checks on the same fabric, see tensile strength.
Related guides#
- Yarn count: the count systems used in the construction line.
- Yarn count conversion: converting counts between systems.
- Knit vs woven fabric: why construction analysis differs for knits.
- Fabric testing standards and methods: construction tests within the full test program.