The US Customs and Border Patrol Agency has awarded contracts to four firms to build more prototypes of the 2,000km wall planned for its southern border, bringing the total number of commissioned prototypes to eight.
These companies were picked to design a barrier that is not made of concrete, which is the material the four chosen last week are all planning to use.
The agency said in a statement that these latest designs would "provide an innovative perspective in the application of new materials which will allow CBP to evaluate the potential for new wall and barrier designs".
The companies are: The Caddell Construction from Montgomery, Alabama; KWR Construction from Sierra Vista, Arizona; Elta North America from Annapolis Junction, Maryland; WG Yates & Sons from Philadelphia, Mississippi.
That brings the total number of companies involved to six, because Caddell and WG Yates were also selected to build concrete prototypes.
Image: Wherever will it end? In Tijuana, Mexico (Creative Commons)