Quadro™ is a medium efficiency gradient filter that is comprised of four different non-woven layers. These four layers from upstream side to downstream side are: Inner Scrim, Electrostatic Layer, MicroFiber Layer, and the Outer Scrim. 
Inner Scrim
The inner scrim is a thin layer of spun-bonded non-woven material. It is situated as the upstream material layer for two primary reasons: first, the inner scrim protects the structural integrity of the down stream layers by preventing mechanical damage (caused by wind shear), second, the inner scrim deflects air flow and reduces particulate momentum in order to create more even and effective filtration by the next three downstream layers.
Electrostatic Layer
The electrostatic layer is a needle punched electrostatic non-woven material. Designed for use as a depth filter with significant dust holding capacity, the majority of particulates in an airflow are captured here by the electrostatic layer.
Micro Fiber Layer
The micro fiber layer is a high efficiency melt blown micro fiber. It serves to trap smaller particles downstream of the electrostatic layer that previously eluded filtration. When used in conjunction with the electrostatic layer, the micro fiber layer can accommodate long life service cycles.
Outer Scrim
The outer scrim is a color coded spun-bonded non-woven material. In addition to providing strength to the filter’s external surface, the color coded outer scrim provides a visual key to Quadro™ media with different filtration ratings.