I would not recommend cotton sock's material; as stated above, nylon sock or panty hose are a better option.

Whatever the filter material is, it gets soaked in oil and fuel, which increases the filtering effect but also the resistance to the intake.

The idea is to use as much surface of filter as possible and rather coarse material.

I use Bru-Line filters in my engines and I heve not noticed any drop in power.

For the same reasons that you explain, RC cars and truck use filters all the time.

Here you can find some ideas of materials and shapes:

http://www3.towerhobbies.com/cgi-bin...=RF&search3=Go