Attention! There are sellers who offer inferior filters that either contain no meltblown fleece at all or only one layer. However, meltblown fleece is the most important (and most expensive) component of these filters. The filters offered here have either two Locations Meltblown fleece or even consist to 100% from meltblown fleece (Polypropylene). But what is Meltblown? Meltblown is a nonwoven fabric made from extremely fine, melt-spun microfibers. These fibers are up to seventy times thinner than a human hair and thus in some cases only one micrometer thick on average. The raw material for meltblown nonwovens are polymers. Why Meltblown nonwovens filter so much better than construction wool cloths is shown by a simple comparison: meltblown nonwovens consist of the finest fibers, which are on average only 1 µm thick and endless in length. By comparison, a cotton fiber is 12 to 35 µm thick and 15 to 56 mm long. In addition, meltblown nonwoven webs can be produced in different thicknesses and densities. For example, a meltblown nonwoven with 25g/m consists of up to 500 fiber layers. Filters made of meltblown nonwoven also combine high performance with good comfort (easy breathing) because a balance can be achieved between separation efficiency, storage capacity and pressure consumption. However, breathing vapour reduces the filter performance, therefore they have to be changed regularly!