It doesnt actually with the one i got (one in the pic) , as its a funnel filter so all you need to do is route the pipe from the front grill to sit insde the end of the funnel filter. Then only cold air enters the filter and it gives you the power increase due to better breathing and the noise as the air spins insie the filter.
My partner noticed the gain as soon as she drove it (and she knows absolutely nothing about cars)
Matt 
Ahh, OK. If you have a sealed duct around the filter leading to a place of coldness that's fine.

Cooler air is far better than having a little restriction.
My argument is that the original panel filter would have been designed with a fair margin of area in reserve to allow for contamination during the long service life so I'd be surprised if a significant improvement would result over a standard filter regularly changed.
there must be some sort of gain otherwise they wouldn't bother selling them!!
But people sell plastic "superchargers" that are no more than hair dryers that bolt onto your car, all manner of additives and potions, magnets that you put in your tank to save fuel, etc. If people can be convinced to buy them, they'll sell them.
Kevin