Permavoid Biomat is a modified Permavoid cell that contains a high strength, low density floating mat to trap oils and other pollutants as they sink under gravity. Consisting of a buoyant plastic grid sandwiched between two permeable geotextile sheets, this mat acts as a 'second line of defence' against hydrocarbon pollution, filtering out emulsified oil and particles too small to have been intercepted by Permachannel processes above ground. It also provides a habitat for the microbes that feed on oil deposits and play a vital part in breaking them down through aerobic digestion. The result is a self-sustaining, self-cleaning water treatment system that needs little or no maintenance and actually becomes more effective over time.

Permavoid Biomat cells are their most effective at key ingress points to the SUDS tank, where concentrations of oil and impurities are at the highest.