The prices aren’t particularly high, and it’s a bit fiddly to attach, but it’s doable because you don’t need any special tools. But the crucial question is, is the whole slide thing even worth it?
In principle, one should not expect miracles from the foils, the advertising promises should not be tenable. Proper insulation of the facade by craftsmen is definitely the better solution.
Frank Ebisch from the Central Association for Sanitary, Heating and Air Conditioning sees it that way too. “Anyone who sticks pure aluminum foil behind the heating does not achieve any insulating effect. A very poorly insulated house can achieve savings of up to 4 percent when using a foil with an additional insulating layer. With modern construction, the reflective foils are not worthwhile”.
If you assume annual heating costs of 2000 euros, you could save a maximum of 80 euros. That would have probably just about covered the cost of the slides in the first year.
The reflective foils are neither a placebo nor should their effect be overestimated. In well-insulated houses without heating niches, however, you can definitely save on the foils.