Fibre Glass OR Low Density Glass Fibre Iinsulation

[Peter Vander Heide]

I'm looking in the Generic North American Database with WUFI 4.2. I know I have run cases using both of these materials in the past, probably making a selection based on density, if I knew what the density was.

Now I'm looking at the two of them for a new problem, and I'm trying to make sense of the hygric extensions.

Fibre Glass, 1.873 lb/ft^3 has no moisture storage function, while Low Density Glass Fibre Batt Insulation, 5.494 lb/ft^3 has a sharply increasing moisture storage function at higher humidity.

Then again,
Fibre Glass, 1.873 lb/ft^3 thermal conductivity, moisture dependent increases from .02 to .35 while Low Density Glass Fibre Batt Insulation, 5.494 lb/ft^3 has a constant thermal conductivity, moisture dependent at .25.

When I run 2 cases to compare them with exterior stucco on OSB, the results are not greatly different, but I do notice that the Fibre Glass case has almost 50% more moisture in the insulation layer even though it has no moisture storage function as opposed to the Low Density which does have moisture storage function.

I know these were compiled from a composite of sources, or just from ASHRAE 1018-RP, but can anyone offer a little guidance about which would be most representative of what is being used in the US.