I wonder how Teflon (PTFE) compares to this stuff. In the DIY multispectral photography community, a lot of people use it as a reference material because not only is it pure white to our eyes, it also reflects (diffusely) UV-A, UV-B, and SWIR very well. I found a chart and paper[1] showing that a proprietary variation of it called Tetratex continued that theme well into the SWIR range, but unfortunately the authors didn't measure it into the MWIR or LWIR ranges.
It's easiest to find at the hardware store as very thin tape for wrapping pipe threads, but I bought a few bars of it (about 5mm x 30mm x 300mm) on eBay years ago, so I know it comes in a form that would be more convenient for making into roofing or siding material. I don't know how it holds up to weather, though. According to that paper, it needs to be at least 0.5mm thick to reflect longer wavelengths, so anyone who's curious about testing it should find the thicker stuff like I did.
It's easiest to find at the hardware store as very thin tape for wrapping pipe threads, but I bought a few bars of it (about 5mm x 30mm x 300mm) on eBay years ago, so I know it comes in a form that would be more convenient for making into roofing or siding material. I don't know how it holds up to weather, though. According to that paper, it needs to be at least 0.5mm thick to reflect longer wavelengths, so anyone who's curious about testing it should find the thicker stuff like I did.
[1] https://www.researchgate.net/figure/Reflection-coefficient-f...