Both the porosity and the permeability of the fiber-mat affect the filling pattern in a Reactive Molding analysis.
The porosity of the preform is described by the following equation: 
where:
-
is the porosity 
is the thickness of the fiber-mat - the values with the subscript
are those at the specified reference thickness
The permeability of the preform is described by the following equation:
where 
is the permeability.