Just finished my DIY version of a Thermoflect UQ. I followed the IXC UQ directions modified to just create the bottom layer. The other difference is that I did not sew but glued in channels using Goop glue. I used material cut out from the neck grove to glue the dart together. The glue worked great but only worked to glue the blue side to a blue side.
Thermoflect seems to have 3 layers - blue layer is soft absorbing material, middle is aluminum and the outer layer is a plastic film. My test will use the blue layer on the outside so any moisture will collect and can be easily poured or shaken for removal.
I am only planning to use this into the middle 50's on a trip to the BWCA and will let you know how it works.