The backing is made of aluminum foil + 2-way scrim/3-way scrim + kraft paper, which has higher intensity than pure aluminum foil. It is mainly used for air-conditioning duct system folder tendons seams and joints. 

Backing: aluminum foil + scrim + kraft paper 
Backing thickness: 110 micron 
Total thickness (backing +adhesive): 165 micron 
Adhesive: hot melt adhesive / solvent acrylic adhesive