[eno_]

Heated metal - e.g. the tungsten in a lamp filament - radiates in a particular spectrum. So I'd bet there is some filter that is tuned for hot aluminum in the seeker. It could be outside the IR spectrum, of course, otherwise lightbulbs would be IR and you would not see hot metals of any kind glow.

[Doe Eyes]

From Post 50:

The 9M313 missile of the SA-16 employs an IR guidance system using proportional convergence logic, and an improved two-color seeker, presumably IR and UV.

This means the missile is tracking a target by using energy in two bands, IR and UV, both of which are produce by an aircraft engine. I believe this technique makes them less vulnerable to electronic countermeasures.

[AdamSelene235]

Heated metal - e.g. the tungsten in a lamp filament - radiates in a particular spectrum. So I'd bet there is some filter that is tuned for hot aluminum in the seeker. It could be outside the IR spectrum, of course, otherwise lightbulbs would be IR and you would not see hot metals of any kind glow.

Many lightbulbs have their peaks outside the range of human vision. ~1.3 um is not uncommon.

Blackbody curves are rather broad. Most heatseakers work in several high atmospheric transmission windows in the mid-IR . ~ 2-5 um.

Oh, and the material doesn't matter, hot AL and hot steel look pretty similiar.