A couple scans from my notes which may be useful.

One discusses alpha energy loss in nominal kitchen foil (~12 um) and also introduces my technique to calibrate a thin (~20 um) SSD.  Sorry I forget which student's thesis it's from, either Sakaguchi of CNS Tokyo or perhaps Dahee Kim of 
Ewha.  They both did alpha measurements in 2015 as memory serves.  It shows we could measure the thickness of the 12.5 um Al foil from Goodfellow with a standard source.

The second is just an email to a colleague about how I went about measuring some foils by weight.  In that case, I want to get an idea on "how much aluminium might be evaporated on the mylar" and I got, I believe, a pretty sensible 
answer.  Of course, I *assumed* that the mylar was the nominal value.