something made of material that deflects the heat away from the filter works best as in the pics above (aluminium, reflectix etc, a mesh with aluminized content). conductive heat transfer is not an issue in automotive applications as it does not affect the intake temp (studies show this...also many after market intakes are made of metal) so...make one out of aluminium if possible. when it comes down to it though, getting colder air into the filter whether it is stock or not is more important than shielding the filter itself.
To give you an idea of how well aluminium works as a heat deflector. I used to have fuel boiling in the carbs of my summer car after hard driving. They were too hot to touch even for a second or two as you can imagine.
I fabricated a heat shield out of aluminium and wrapped it just below the 3 carbs, separating the carbs from the headers with the aluminium. Now after running the car hard, in hot weather I can leave my hand on them, totally cool to the touch.
