Physical barriers are so-called because they rely on the physical resistance of the material to resist termite attack. These are usually installed during new constructions, but some can be retrofitted to existing houses. Barriers can be placed under concrete slabs, foundations, and within cavity walls.
Physical barriers are made from metal, crushed rock, or other materials that termites cannot chew through, and in which any gaps are too small for termites to move through. Most of these products have to be installed by professionals who are licensed by the manufacturers.
Ant caps are installed at the top of underfloor piers or stumps to force termites into the open where they are easier to detect during regular inspections. Ant caps are not a barrier by themselves.