What air filters makes are most popular and why?

[MikePCG]

Just a general interest question.

What air filters are most popular amongst Motorsports such as BTCC etc. I Don't know anything about their engine setups and just wanted to know what type of setup they go for and most popular filter makes, such as K&N / ITG / Pipercross or do they have them custom made etc.

[Megaflow]

AFAIK they are custom made for the application, but they are made by one of the mainstream manufacturers. Last time I saw an F1 air filter it was cotton gauze type, like K&N.

[PhillipM]

Green Cotton usually do a lot for the WRC and I think they used to do mclaren's filters for the F1 too.

[RB Will]

I'm very possibly wrong but don't K&N advertise as having won more races than any other manufacturer?

I have had K&N induction kit on 2 of my last 3 cars, other one was a Cosworth panel filter. None gave me any problems. I presume lifespan and ability to clean them are good reasons to buy.
Had a Blitz one on my old Scoob and had to throw it away as the oil from it was knackering my MAF.

[DanDC5]

ITG are pretty popular in the BTCC I believe.

[MikePCG]

Yeah seen a few pics with ITG being used and a few with Pipercross filters, mostly from BTCC cars, but what date these pics were taken, I'm not sure. cheers.