The consequences of humidity exchanges between food and environment ar
e always very important for the preservation of microbiological and se
nsorial quality of the product. For a realistic shelf-life evaluation
of sensitive food-products is therefore essential to know exactly the
water vapour transmission rate (WVTR) through the packaging material.
The measurement of this important diffusional property is commonly per
formed without regard of the exchange direction and in conditions very
far from those of reality: extremes temperature and humidity combinat
ions as 38 degrees C and 90% of U.R. Thus, it was considered useful an
d interesting to verify if the permeability phenomenon could be affect
ed by the direction of flow and by the contact of dry or moist product
. To such purpose measures of water vapor permeability were realized u
sing PET and OPP pouches, filled with water or Calcium Chloride. The r
esults achieved excluded the influence of the contact of dry or wet su
bstance with the pouches walls and of the now direction on the determi
nation of the WVTR for the materials and the conditions examined.