Reflectix does block heat when it's installed with the reflective side facing out and keeps the heat from entering past the Reflectix.
When installed correctly Reflectix does keep heat out and blocks the heat from entering through windows and other places it's installed and can keep the room cooler as well.
In winter the Reflectix when installed correctly can also keep the heat inside of the place it's installed.
Reflectix is good for winter as well as summer.
In the winter Reflectix when installed correctly can keep the heat inside the home or place that it's installed in and in summer it can keep the heat out of the room or place it's installed in.
The side of Reflectix that faces out is the reflective side in summer to reflect heat away from the space.
However in winter and cold conditions you want the reflective side of the Reflectix facing inwards to reflect the heat back into the room or space.
You want to install the Reflectix so that the reflective side of the Reflectix is facing the area that you want to protect from heat or the cold.
Reflectix works by reflecting the radiant heat, both infrared and visible light instead of absorbing it.
And an air gap is crucial with Reflectix.
In order for the Reflectix to effectively reflect the heat, an air gap is needed between the surface it's facing and the reflective surface.
Also the direction matters when installing Reflectix depending on the temperature.
In summer and hot conditions you should place the reflective side of the Reflectix facing outwards to reflect the heat away from the space.
And in winter and cold conditions you should place the reflective side facing inwards so that the heat is reflected back into the room or space.