The most lucrative source of Feltrite comes in the form of the supply crates you find at bandit dens and abandoned areas. You will also find clusters of Feltrite protruding from the walls of these same areas. These are worthwhile pulling out of the walls they grow on as they yeild 24 Feltrite a piece. Feltrite can be found inside the brown Feltrite Crates and by shooting enemies who will drop a small amount when they are killed.