There are cracks up to a quarter inch wide between the the window
frame and the inside window trim. It had been letting in cold air and
leaking out warm air out for years. I had not done anything because I
tolerate cold better and always set my thermostat to 72 deg F. The
average gas bill hasn't changed for years and the furnace wasn't
exactly knocking itself out unless it gets to minus twenty deg F or C.
Its an unreliable measure of energy loss for sure.

The window frames were tight and secure to the stucco finish so there
were no repairs or caulking possible there without making the problem
something major. Same thing inside the house. The window trim was
also tight and secure against the wall. No adjustments were possible.
I didn't like the idea of those aerosol cans of squeeze foam
insulation as they are sticky and would be impossible to remove if
they didn't work and I come around to redoing the window repairs.
This is indeed fortunate because I chatted with my neighbor and he
said never to use that stuff. He did and the foam accelerated the
cracks in his windows over the years and he has a real problem now.
My other porposed solution was to stuff the cracks with fiberglass
insulation and glue or nail a thin slat of woodover the whole inside
window trim to cover the repairs. I have a well equipped garage
workshop and can do that except I procrastinate (long story).

On saturday my sister stayed over (I live alone) and refused to sleep
in the leaky cold bedroom preferring the sofa. By the morning she
insisted on fixing the cracks and asked for those 1/4 inch rolls of
sticky backed foam tape weatherstrip to at least temporarily close the
cracks. Then she found I had leftover laminate flooring underlay foam
sheet scraps. She used these instead and they are an excellent
material as they are formulated for years of servive as flooring
underlay. They are also strong and flexible and therefore will
conform and fill the cracks to the edges. I love the solution. I
wasn't too impressed with the foam weatherstrip material as they lose
their elasticity and therefore seal effectiveness after a season or
two. They are also hard to trim to size to fit the cracks.

My next step is to find a roll of self adhesive vinyl shelf liner
contact "paper" with a suitable design and use that to finish the
window trim and cover the cracks. Sis had asked for duct tape or
transparent box tape, a pretty ugly, temporary idea (they dry up and
deterioate) that leaves a messy residue when its time to remove them.

I am a pretty happy man. If this fix doesn't work I can easily undo
everything without risking a messy cleanup. But I am confident that
the fix will be good for years and I can always do the same fix at
some future time should that become necessary.