A new honeycomb attachment for 80/92mm and 120mm fans has been introduced by a Netherlands company called NEXUS. The Nexus BeamAir is an adapter you place over your case fan that improves air flow. The honeycomb structure straights chaotic airflow and improves pressure drop. The BeamAir's suggested end user price is only € 4.35 for the 80/92mm and € 4.91 for the 120mm version. Aluminum honeycomb "flow straighteners" are used in wind tunnels, yet while the Nexus BeamAir is hardly comparable to a mesy of 1/4" cells, according to documentation we've seen it will improve exhaust airflow from the case fan.
