It is very common to use expanding foam to plug those holes. Red putty
sounds like fire caulk. You don't need fire grade caulk in a wood stud
wall, but fellas probably had some if they did much commercial work.
You could use any type of caulk - there is no requirement for anything,
it is only performed to help prevent drafts and help the HVAC. If the
holes are very large with a large annular space, it may be much easier
to stuff them with rock wool.
Agreed, it was common to use expanding foam for this purpose up until
the building code changed a couple of years ago, now it is required to
use the rated and approved means of fire stopping in all of those
Unless your jurisdiction is still using and applying an older version
code in their area...
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