ISO 105 B02 is the world’s most widely-used textile lightfastness test. This standard was originally written before precise control of temperature and humidity was readily available in weathering testers, and like other standards it uses reference materials to compensate for this. ISO 105 B02 requires the use of a humidity test control fabric to verify chamber humidity during testing. This is a piece of wool dyed with a red azoic dye. The lightfastness performance of this fabric is largely dependent upon the humidity in the chamber. As the moisture content in the air increases, the lightfastness of this fabric decreases. By comparing the performance of this fabric to the blue wool control material used in ISO 105 B02, one can approximate the humidity in the chamber using the following figure:


Blue Wool Lightfastness Rating of Humidity Test-Control Material v. Effective Humidity

How to Perform the Humidity Test
In order to perform the humidity test, you will need both blue wool reference material and the humidity test control fabric. The types of blue wool used in the test depend on which cycle you’re running:



The humidity test control fabric and all of the appropriate blue wool reference materials are mounted on white cardstock and covered with a mask. The test is then run until the humidity-test control fabric achieves a grey scale of 4, and its performance is compared to the blue wool references. If the humidity-test control fabric has a similar performance to the blue wool indicated in the table above, then the tester meets the requirements and can be used to run ISO 105 B02.