The Polygareg; humidity measuring element consists of several synthetic fabric bands each with 90 individual fibres with a diameter of 3m each.
In their untreated state, the synthetic fibres are not hygroscopic – their hygroscopic properties are acquired by means of a special process which allows the synthetic fibres to absorb moisture.
The molecular structure of the individual fibres is arranged lengthways. When water is absorbed, the molecular chains alter, the outward result being a change in length. A loss of water has a converse effect on the fibre.
If the fibre is in equilibrium with the air humidity, there is neither absorption nor a loss of water. The length at this point serves as a gauge for the relative humidity.