Filbert With Involucre: The Iranian Filbert nut is 4 CM long and enclosed in a papery covering referred to as an involucre. Filbert Fruit Persian Walnut Filbert Without Involucre: Iranian filberts, also called hazelnuts, are rounded and slightly pointed at one end. They are small, usually about 3 CM long, and resemble an acorn with its top removed. Filberts have a thin but strong shell that is shiny and golden...