We have a stack of 4 inch rigid foam board to use in the attic. This looks like a lot cleaner method of cutting rigid foam insulation board than the messy table saw or kitchen knife..........
I suppose if you didn't have a lot then you could do it like they did it on Fine Homebuilding
http://www.finehomebuilding.com/how-...nsulation.aspx
But I like this way best....