If memory serves me correct, most modern thermal imaging system use a combination of materials such as InSb, HgCdTe and PtSb. The range of detectable infrad range from 1um to 5um depending on material design. The ability to see through smoke actually depends on how hot the smoke is. For hot smoke generated from burning tires, it's not good. However, most military smoke are generated by chemical means, and do not have a infrad absorbing spectrum across detectable wavelength range. Modern thermal image devices are highly sensitive when cooled. Most design issues are optics rather than electronics.

AIUI, there are two primary bands for thermal imagers, one of which was better resolution, but blocked by atmospheric water, or something.

"If memory serves me correct, most modern thermal imaging system use a combination of materials such as InSb, HgCdTe and PtSb. The range of detectable infrad range from 1um to 5um depending on material design"