Nutricost's Colloidal Silver contains 30 ppm per dose of pure Colloidal Silver. Nutricost packaged this in Cobalt Blue glass bottles to protect the bioactivity, the effectiveness, of the Colloidal Silver liquid. The blue glass filters UV light which can compromise the stability of the Colloidal Silver. Plastic can affect the charge of the silver ions in the liquid. Maintaining the stability of the Colloidal Silver can help its bioactivity, its effectiveness in being absorbed and used by the body.