Ha ha good one.... TP, good is always better. Recycled cardboard = pain.

I think this debate is moving into science not application installation procedure. Yes, everyone agrees that filtration media will function forward or backwards to air flow and it will remove airborne particulate matter down to x.x microns. I think the OP question was which way to install the preformed panel filter. If he is using the Mann charcoal impregnated ones it makes a big difference on filter effectiveness and life span.

Air flow is up.

__________________

2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green