Would a sheet of aluminum or sheet of stainless steel reflect more infrared radiation

[ircasodle]

First of all, to have good reflectivity in the IR part of the spectrum, you need to have very flat surfaces, so you will need a polished surface. Stated that, Aluminium has far better reflection than steel. When not oxidixed. You can have reflectivities of up to 97%, with 92-95% easily attainable, while with steel a reflectivity of 90% is a very good value. Unfortunately, the reflectivity of oxidixed aluminium can be as bas as 70% and unprotected aluminium oxides much faster than stainless steel. The ideal solution is a properly treated aluminium foil (or a plastic foil with deposited aluminium). The only place in which I'd use steel is for a second of a two stages concentrator, in which temperatures could rise so high that you need a metal alloy without any plastic (either substrate or varnish). For that applicaiton, I'd go for stainless steel sheets.

[KamorkasOa]

You'll have to be careful with the emissivity values. The values may not take into account that you're likely to have an oxide layer or dust or whatever that builds up on a surface that would change the emissivity. Your effective emissivity may be less or not what you expected. Also, infrared is less sensitive to surface roughness than is visible light, because it is a longer wavelength. That is, the surface might be not perfect in visible light, but be pretty good in effectively concentrating infrared. We did this experiment once in my Heat Transfer class where we used a plate of cold-rolled steel as a "mirror" for an infrared camera. The image was the same with the plate of steel when compared to a regular optical mirror.

[askaluadmin]

I am no expert in this, but as I think of aluminium wrap against steel foil, i see that aluminium reflects heat (can i use this synoymous to infrared here?) better.