My contractor is using EnerFoam by DOW to insulate the around the frames of
my inserts. IS this the proper stuff to use. I alwasy heard that the stuff
to use should be non expandable, but the stuff he used is definitely
expandable stuff.

Is this the right stuff? He already has done 2 our of 15 windows and the 2
windows that he used the EnerFoam stuff work well. One is a vertical slider
and one is a casement. My concern is that they will bow over time. If they
didn't bow now can they still bow over time?

Should he be using non expandable foam? If so what is the best product(s)
he shoudl be using?