Smoked gray will likely pass IR from an IRED. In fact, I use a piece for an IR window on a device I made years ago. When you ask about IR transparency, you need to add a little more information, like at what wavelength. When you ask about "filtering," do you mean you want it to pass IR and block visible, pass visible and block IR, isolate a particular IR wavelength, just block IR without regard to other light, etc?