Polyester Yarn Shrinkage test

The shrinkage of yarn is a reduction in the yarn length due to heat treatment. The pre- and post-treatment yarn lengths are measured under a certain tension and reported as a fraction of the initial length. The results could be useful in predicting the dimensional stability of textiles in high-temperature heat treatment and washing.

The shrinkage of yarn can be measured and reported in different conditions, e.g., boiling water, hot dry air, saturated steam, or even superheated steam.

The SIRANG lab tests the shrinkage of yarns in boiling water and hot dry air. The test equipment includes a wrap reel machine, a boiling water bath, a high-temperature oven, and a yarn length measurement device.

Shrinkage of Yarn Test Process

The yarn hanks are first placed on the holder, and the initial length of the sample is measured and saved by a shrinkage tester. Depending on the test conditions, the yarn samples are placed in the boiling water bath at 100±3°C or the oven with hot dry air at 190±3°C for 30±5 and 15±1 min, respectively. The yarn samples are taken out, waiting until they are cooled down to measure their final lengths. The tension applied to the yarn is set to 0.05 cN/dtex. The shrinkage of yarns is measured as a percentage based on the initial and final lengths by the software program.


  • The typical standards are ASTM D2259, ISO 18066, and ISO 18067, whereas the national standards are ISIRI 20095 and ISIRI 20096.
  • An automatic wrap reel machine is used to make yarn hanks. The boiling water bath has a sufficiently large width and depth, and the holders are fastened in the bath.
  • The high-temperature oven can supply hot air at up to 200°C. The yarn length measurement device can automatically apply a certain tension to the yarn samples and measure the yarn length with a resolution of 0.05 mm. The software of the machine calculates the shrinkage of yarn based on the measured initial and final lengths.
  • Shrinkage testing can be conducted on hanks and single strands both manually and automatically.
  • To measure the shrinkage of FDY yarn 500 dtex, hank samples are wrapped, implementing the shrinkage test of polyester yarn under the relevant standards and wrap reel machine (10-round hank).
  • Iranian National Standard No. 925 proposes a maximum shrinkage of 15% for FDY yarn.