This is the TWIR AIR air filter. 
A first layer of airy foam traps dust, sand and impurities. Denser, the second layer of foam stops the finest particles while promoting the passage of air flow.
Twin Air filters are significantly smaller than the original ones in order to increase the volume available in the air box and thus promote air circulation.
The bonding of the two foam envelopes between them eliminates the risk of dust and impurities being placed between the two layers.
Gets on: 
HM CRF 230 F 230 2013 
HM CRF 230 F 230 2012 
HM CRF 230 F 230 2011 
HM CRF 230 F 230 2010 
HM CRF 230 F 230 2009 
HM CRF 230 F 230 2008 
HM CRF 230 F 230 2007 
HM CRF 230 F 230 2006 
HM CRF 230 F 230 2005 
HM CRF 230 F 230 2004
HONDA CRF 150 F (KE01) 150 2005 
HONDA CRF 150 F (KE01) 150 2004 
HONDA CRF 150 F (KE01) 150 2003
HONDA CRF 150 F (KE02) 150 2019 
HONDA CRF 150 F (KE02) 150 2018 
HONDA CRF 150 F (KE02) 150 2017 
HONDA CRF 150 F (KE02) 150 2016 
HONDA CRF 150 F (KE02) 150 2015 
HONDA CRF 150 F (KE02) 150 2014 
HONDA CRF 150 F (KE02) 150 2013
HONDA CRF 150 F (KE02) 150 2012 
HONDA CRF 150 F (KE02) 150 2011 
HONDA CRF 150 F (KE02) 150 2010 
HONDA CRF 150 F (KE02) 150 2009 
HONDA CRF 150 F (KE02) 150 2008 
HONDA CRF 150 F (KE02) 150 2007 
HONDA CRF 150 F (KE02) 150 2006
HONDA CRF 230 F (ME09) 230 2019 
HONDA CRF 230 F (ME09) 230 2018 
HONDA CRF 230 F (ME09) 230 2009 
HONDA CRF 230 F (ME09) 230 2008 
HONDA CRF 230 F (ME09) 230 2007 
HONDA CRF 230 F (ME09) 230 2006 
HONDA CRF 230 F (ME09) 230 2005 
HONDA CRF 230 F (ME09) 230 2004 
HONDA CRF 230 F (ME09) 230 2003