GOOD testing! Just on a more theoretical concern, I am not sure that multiple layers of foil/mylar space blanket will change your numbers significantly during measurement. Once the IR radiation has been reflected, there will be nothing left for a second layer to reflect. You would still get some, of course, due to the space blankets own warmth, more on that part below. A second layer will help slightly, but I doubt you would be able to measure the difference with your equipment. I suspect a NeoAir Xtherm is simply holding dead air better, hence, increasing it's insulation effect, not so much the second layer reflecting more heat back. Besides, the reflected radiation would be trapped between the two layers, effectivly just warming the air molecules slightly.
"Both combined gave a 20 degrees F difference, but I was pushing the limits of my instrument because there was so much temperature difference, that the torso temperature was much greater than 93 degrees F, so there was more radiant and convective heat loss around the edges and my guard plate wasn’t able to get warm enough, so I question this result."
Yes, I would question this result, too. But, you are ignoring the actual warming of the "space blanket", as above. This will cause it to radiate IR the same as if it were reflected. Containing little mass, it will re-radiate warmth almost as quick as it absorbes heat. Heat is defined as the movement of molecules. IR is defined as a radiation. Heat is what we get when IR is absorbed. IR is what we get when heat is lost (if not by conduction or convection.)
Outdoor Wilderness Fabric (http://www.owfinc.com/) still has some UV reflective silver and white.
As far as mylar films go, they aluminize the mylar films by passing through a chamber that is evacuated. A jolt of electricity flashes off aluminum from a bar stock that coats the film, 2-5 molecules thick...read very thin. It is not physically adhered to the film, so it will wipe off with use. Not very durable.I suspect that aluminized cuben would be no more durable, since it would prevent the inside surfaes from bonding with pressure. It would need to be applied to the outside, much like a typical space blanket, and, have the same durability issues.
For breathable, perforated mylar, a sheet *could* be folded quite small and clamped between a couple layers of 1/4" scraps, then using a 1/16" (a bit more than 1mm) just punch a series of holes through it. I haven't tried it, but I would guess it would take no more than 15 minutes to do.