Metal grill - optimum pattern for air flow?

[ewizard]

I have a buddy that owns his own CNC fabrication company.
I was going to have him cut out some custom shaped metal grills for my future IB installation.
What type of pattern would give me the best air efficiency for a 2x18" manifold approx. 20x14"?
If it's a pattern, what percentage of material should be removed?

[ThomasW]

The best material for manifold openings is a single knit polyester.

I don't imagine there would be any significant audible differences to patterns cut in metal provided the ratio of open area to closed area remains the same