This reduces heating costs

The film or wall insulation is glued on the back with Styrofoam.
That's the only thing that bothers me. The film is thus not flexible, but breaks.
Too bad, that should improve the manufacturer.
Just behind the radiators which is quite a fumbling and you have to bend the foil up and slide, so you even get behind the radiator.
My film is broken at a corner, when I undertook the very first attempt to bring the foil behind the radiator. I've now just recognized with double-sided tape to the breaking point.

For sure I will not, as suggested, glue the foil to the wall, but I had first worked with thumbtacks, but that did not please me, and then I switched to double-sided tape. This goes quite well.

You can tell really like the heat of the heater is thrown back into the room and not the wall is warmed. So cold it was now (October) not yet, but the first tests are promising. You have to turn on heater less (3) and has more heat.

Will still try a little and then me again reorder sheet to provide all radiators with it.

Had the film flexible without breaking, it would get 5 stars.
Otherwise great idea. And the price is also ok.

Addendum on 10/10 .: you can clearly see the difference: Because where I installed foil behind the radiators, it is felt quickly than in the radiators that still do not have film. The radiation in the room is good.

Addendum on 10:11 .: The film is worth total. It will warm up more quickly, clearly! And you have less turn up the radiator.

Addendum 22.12 .: I have to turn up no more radiator on Level 3, the heat is there, the reflective effect also. Great Thing