truck bed liner underliner

A truck bed liner underliner is a mat installed between a drop-in plastic bed liner and the truck bed floor. Its primary purpose is to prevent the moisture and debris that accumulates under a drop-in liner from accelerating rust on the truck bed surface. Drop-in plastic liners can trap water and road salt against the painted bed floor, which is one of the leading causes of truck bed corrosion on vehicles used year-round in Canada. An underliner acts as a moisture barrier and ventilation layer that reduces this risk significantly.