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It is a common practise to
measure the permeability to the vapour, for covers with a
polyurethane coating. These coated textiles were naturally and
totally permeable to the vapour. This permeability was an
interesting indicator of "breathability" (treatment having as
consequence micropores in the polyurethane coating) and consequently
a factor of comfort.
This indicator is not useful now
with non-coated textiles, which constitute an efficient barrier
against dust mites thanks to their weaving /manufaturing process and
not thanks to an additional chemical coating. Consequently, the non-woven
textiles have pore sizes,enough small to trap dust mites and, enough
big to be naturally permeable to the air.
That is the reason why, you will never find
this indicator among manufacturers,
who use woven textiles without coating, such as Texaal®,
or non-woven textiles without coating, such as Evolon®.
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Covers manufactured in non-coated
textiles, such as Texaal Cotton or Texaal Polyester or Evolon, are
naturally permeable to the water vapour. The indicator of
permeability is useful only for materials that got a specific
treatment, in order to become permeable to the vapour.
That is the quality of this
treatment, which is measured.
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