One roll of 400 by 45 cm, about 1,8 square metres, at EUR 17.99, rated 4,6 from 113 reviews. Milieu Centraal counts per square metre: an uninsulated brick outside wall saves about 15 euro a year, an insulated one about 1,40.

What you need to know

The heating goes on in October and a lot of people head straight out for a roll of foil to stick behind the radiator. Whether that wall is insulated decides whether the 17,99 euro comes back in eight months or in seven years, a difference of nearly tenfold, and the product page never asks the question. The specification block on this Nordevik roll gives 400 by 45 cm, roughly 1,8 square metres, with 20 magnets that hold it against the back of the radiator. It is rated 4,6 from 113 reviews.

Milieu Centraal publishes the yearly effect per square metre of foil, calculated at a gas price of 1,37 euro per cubic metre. Against an uninsulated brick outside wall it saves 11 cubic metres of gas a year, around 15 euro. Against an uninsulated cavity wall it is 7 cubic metres, around 10 euro. Against a wall that has already been insulated it drops to 1 cubic metre, around 1,40. Where the radiator sits in front of glass the numbers change completely: 50 cubic metres, around 70 euro, with single glazing, and 25 cubic metres, around 34 euro, with double.

Applied to this roll: 1,8 square metres times 15 euro is 27 euro a year, so 17,99 comes back in about eight months. A cavity wall gives 1,8 times 10, or 18 euro a year, roughly twelve months. An insulated outside wall gives 1,8 times 1,40, or 2,52 euro a year, which takes over seven years. So the step before ordering is to establish what that wall is: the building year, whether cavity insulation was ever done, and the energy label from the sale or rental file usually answer it.

Separate wall from glass first: the foil holds back the heat that escapes behind the radiator. It earns its place against an uninsulated outside wall, while against an already insulated one the yearly return is 1,40 euro per square metre and the fitting time costs more than the saving
Trust the specification block for size: 400 cm long, 45 cm wide, 20 magnets included. This page's web address still carries an older 500cm wording, so where the two disagree the specification is the one to read
Rated 4,6 from 113 reviews on the bol product page, read 29 August 2026, at 17,99 euro with no strike price shown, which means this is not a discount item and there is nothing to wait for
Measure once before ordering: multiply the width of the radiator by its height for the area, divide by 1,8, and you know how many radiators one roll covers; offcuts do a smaller one

Wipe the wall and the back of the radiator before fitting, because magnets slide off dust. Orientation matters too: the foil belongs between radiator and wall with the reflective side facing the radiator, since putting it on the front of the radiator simply keeps the heat out of the room.

The foil link on this page is an affiliate link: order through it and Hokimi may receive a share, while your price stays the same.