James Marco sent me a sample of aluminized silnylon
David Drake sent me a sample of alumized Cuben
The aluminized silnylon is gray, a little shiny, like the aluminized silnylon I got from Seattle Fabrics years ago that they have discontinued.
The alumized Cuben is shiny, just like aluminum foil. One side is shinier.
I rebuilt my insulation measuring instrument from http://www.backpackinglight.com/cgi-bin/backpackinglight/adams-torso-simulator.html except I re-made the guard ring so it better matches the measurement plate. Maybe I'll write something up about this in the future.
I have this thing about fulfilling commitments, so since they took the effort to send me the samples, I wanted to measure and publish the results.
First I measured some breathable nylon and some aluminum foil. I had some 2.5 oz Apex underneath. I measured the temperature difference between the measurement plate at the bottom of the insulation and the air:
breathable nylon - 36 F
aluminum foil - 46 F
so, with aluminum foil instead of non-IR-reflective nylon, there's a 10 F increase - my sleeping system would be 10 F warmer.
Next, I assumed emmisivity of 0.9 for the nylon and 0 for the aluminum foil. This is just an approximation. Really, the temperature difference is all I can claim from this, and even that is a tricky measurement.
I measured with the alumized Sil and Cuben and measured temperature difference. I then interpolated to determine emissivity:
aluminized silnylon - 42 F - 0.35 emissivity
aluminized Cuben - 40.5 F - 0.5 emissivity
This is really surprising to me, because the Cuben is so shiny, I assumed it would have low emissivity like aluminum foil.
This was just one measurement on one night. It was only about 20% clear and 80% cloudy. I'm going to re-measure if there's ever another clear night, measure a couple times to verify repeatability, measure both sides,... Maybe what appeared shiny to me is actually the mylar side, and the less shiny side actually has lower emissivity.