If you’ve got a BMW 800 or 1200, Guglatech has the perfect air filter for you.  These filters are reusable for the life of your bike.  They meet or exceed OEM specs and provide better filtration than any other design, including paper, cloth, or foam. 

This technical report tells the story:  Air Filter Blog 2

This photo shows a brand-name cloth filter that allowed dirt to pass into the intake manifold.  If the filter had done its job that manifold would be perfectly clean.