Foilboard is a foil lined rigid insulation product which can be used in all different walls construction types. Don't use the manufacturers R-Values claims when interpreting a product not set within the current BERS wall construction library, this is because BERS Pro also takes into account internal and external air films so you don't need to add these in.
For the purpose of this example we need to work out how to model 20mm Foilboard within a cavity brick wall.
Firstly enter the product type and thickness within the Simple R Calculations, located within the Calculation Tools button = R0.5128
In BERS select a reflective bulk insulation - with an air gap to allow for the Bulk + Foil, reflective One Side, Anti-glare the Other - as per attached example.
Follow this procedure if the product is 15mm or 10mm and based on a different construction type.