Conversion of water vapour diffusion values

[Iain McIver]

Hi All,

I just had a quick question on converting MVTR values to something that I can use in WUFI. I understand that MVTR values that are given in MNs/g can be converted to sd values simply by dividing by 5.1.

However I have just been given some data for a product which states that the MVTR of the product is "0.39 g/m^2 @ 24 hours" and gives the reference of ASTM E96

Does anyone know how to convert this to an sd value? can it be converted to an sd value?

Thanks
Iain

[Manfred Kehrer]

Hello Iain,

your value represents just a moisture flow, but there is something missing, the vapor pressure difference.

According to ASTM E96 the results should be stated in perm or g/m2sPa and the thickness of the specimen should be stated as well. Then it is possible.

Get the standard! You will learn a lot.

[Iain McIver]

Thanks Manfred,

I will get back in touch with the manufacturer for that extra information, I will also try and get my hands on a copy of the standard

Thanks
Iain