Whats material is used between a fender and inner fender

Leaves and mud? Thats all i ever find when i look in those places....

DumDum is also referred to as body caulking. I have a tube of this putty that is over 20 years old, cut off a chunk and plug holes or seal panels before bolting together.
Butyl tape was also used,for a lot of things including bedding windows.