I've placed aluminum heat reflectors on walls, behind radiators. As the reflectors were quite visible I've painted them the same color as the walls. Now I'm not sure it was a good idea. Do they still reflect the heat ?
In other (poorly chosen) words: does the reflecting ability of an aluminum panel come from its surface pattern or from its core material ?
Probably not. Reflection is a process that happens in the surface.
Think about mirror. It reflects visible light. Now if you paint it, does it reflect visible light anymore?
Heat reflectors are simply reflectors for infrared radiation. It's similar to visible light but has somewhat longer wavelength (lower frequency).
If the paint is white, it's far better than if it was black, but still worse than the bare reflectors. Anyway, white-painted reflector isn't any better than a white wall.
I put white factory painted aluminum sheeting behind my wood burning stove. Had to replace it with unpainted aluminum because it got very hot. Unpainted aluminum stayed cool. Aluminum foil works but it doesn’t look nice.
