Thank you, thank you Buffalobill.

That's just what I needed, That low density, slow drying, foam.... The
regular foam would blow my drywall off...

Now all I need is to find out if I do put it in MY walls... would it
sink all the way down to the unit downstairs? Typically would there be a
stud? / barrier? in the exterior walls? to catch the foam and keep it in
my walls at my level....

Thanks again BB....