Here is a very rough go at measuring the actual heat loss performance of the bubble wrap:

Oct 24, 2005

I attempted to measure the change in heat loss as follows:

I used two identical, side by side windows.  My windows are double
pane low-e.  I put the bubble wrap on one of them, and let it dry for a
day.  I shut the heat vent in this room, so the inside air temperature
would be more consistent.  I measured the inside ambient air
temperature, the temperature on the inside surface of the glass, and
on the inside surface of the bubble wrap, and the outside ambient
temperature.
I used a Raytek IR temperature gun with a small piece of tape on
the surface where I took the temperature measurements (to keep it from
getting confused by the non 0.95 surface emissivity).  I also measured
the same temperatures with a low mass, surface type thermocouple.
This was all done with no sun on windows.

The TC and IR measurements were close, and showed the same differences.

Troom          67F     (room temperature)
Tbubblewrap    60.5F   (inside surface of bubble wrap)
Tglass         55.3F   (inside surface of glass)

If you assume that the airfilm next to the inside surface of the glass
or bubble wrap has an R of 0.65, then knowing the inside surface
temperature, and the room temperature you can calculate the heat flow
with and without the bubble wrap:

Qnobubble = (67F - 55.3F)/ R0.65 = 18 BTU/hr-ft2 out of the room

Qbubble = (67F - 60.5F)/0.65 =  10 BTU/hr-ft2 out of the room

This amounts to an  (18-10)/18 = 45% reduction in heat loss.

I was expecting that (at best) it would go from about R3 for the
double pane low-e to about R4 for the double pane low-e plus bubble wrap -- this
would give a 25% reduction in heat flow.  So, maybe bubble wrap is a
little better than just adding one extra layer of glazing?  Or, my
measurements could be off a little?  Or, maybe my thinking is off a
little :-) ?

...

Gary