I've central heating (water) radiators close attached to outside walls. Max temp is 90C or 195F. Fiber bats, foam plates etc all come with an optional reflecting layer. For the reflective layer to be of any use it's not allowed the heat source. Is that correct? If so is there a rule about the minimum distance? Foam boards likely don't melt from the heat. But still I would like to know they are advised at that heat level. I must add most of the time it won't be hotter than 60C or 140F I want it be 'safe' for the extremes. To summarize: a] Minimum distance between radiator and insulator. b] Are foam boards a smart option in my situation?