Fuel filter cartridges from previous years have a solid construction with high compressive strength and high resistance to temperature changes, similar to oil filter cartridges. Metal bottoms and inner core are made of perforated metal which assures construction stability and protect the filtering medium from deformation and damage. The additional protection element, often applied is an inner filter medium casing made of perforated paper. It protects the pleat tops from mechanical damage, separating the pleats and making them more rigid. The high utilization cost of these cartridges caused the trend in replacing traditional models with "ECO" cartridges, which do not contain metal parts. These cartridges have become standard equipment in many types of modern engines, both in cars, trucks and machines.