A BGM is a composite material with several constituents to attain the desired overall material properties. They typically consist of non-woven geotextile and glass fleece or polyester layers impregnated with and encapsulated in elastomeric bitumen, with a sanded surface on one side for enhanced friction and an anti-root layer on the other. The geotextiles dictate the mechanical properties of the BGM, while the elastomeric bitumen provides waterproofing, chemical resistance and protection from ageing. The glass fleece is used for manufacturing purposes. It ensures stability of the geomembrane during impregnation of the geotextile with hot bitumen.
Special care is required when unloading and storing a BGL. Specially prepared laydown areas are required with special support for the rolls to prevent deformation of the material before the laying process is commenced.