Permeance is an important property for paper grades like tissue and sack paper, but also for filter products made of cellulose or other fibre materials. For all grades where permeance is important is it also important that the permeance variation is as low as possible. The permeance of a product is controlled by every step in the paper making process from stock preparation to calendering. 

A low variation of the local permeance across the plane of the sheet is often more important than the mean value itself. Regretably, the available standard methods, such as Bendtsen and Gurley, are quite insensitive to permeance variations.

In order to determine local permeance variations, and to perform measurement on materials with high permeances Innventia developed a new measuring device and method. The principle is similar to the one used in the Bendtsen standard method, but the measuring head is small, having a dimater of 2 mm. The new instrument at Innventia measures the permeability of an A4 sample at some 6000 positions. The measurements are interpolated to obtain a two-dimensional map where it is possible to see variations and localise any possible problem areas.

Local permeance map of a commercial liner sample.