These mantra bracelets are filled with silver leaf, this is the silver viriant off the goldleaf. They are closed with a mantra and blessed in the temple. Silver is a young metal , that's why this silver variation is symbolising youth.
The silver leaf has been sprinkled into the flexible tube off the bracelet.
They are water resistant and the silver will age very nice in time, so the longer you'll where it the better it will look.