Meta-materials are advanced technology being researched by DARPA. The materials bend light around objects making things covered by them appear invisible.
Season 4[]
When the Phoenix team infiltrated the DARPA facility during their red cell assignment they started investigating the technology in the facility. The Meta-materials. Russ Taylor seemed particularly interested in the technology because of similarity to an invisibility cloak. After the team accidentally fed off an alarm Mac and Russ hid behind the Meta-materials which obstructed them from the guards’ view.