Absolute degree of filtration

Absolute degree of filtration refers to the fineness (particle size in μm) from which a filter medium almost completely retains all particles of this size and larger. In contrast to the nominal degree of filtration, where only part of the particles are captured, an absolute degree of filtration guarantees a fixed separation rate – often >95% of the particles of the defined size, for example. In practice, this corresponds to the largest possible particle size that can still pass through the filter medium, while 100% of all larger particles are separated.

In industries with high purity requirements (e.g. pharmaceuticals, microelectronics), an absolute filtration efficiency is crucial to ensure that no particles above a critical size enter the end product. Filters with absolute filtration efficiency ensure consistent quality and process reliability, but are often more expensive or finer than filters with nominal efficiency. Typical applications are sterile liquid filtration, hydraulic filters or fine filters in water treatment, where reliability is paramount. In architectural applications, this term hardly plays a role, as filtration properties are rarely the main focus there.