Emergency Blankets:
These are ultra thin polyester blankets that are sold in most camping stores and are constructed of a single layer of polyester film that is covered with a layer of vapor deposited aluminum.
It is not very effective at reflecting light because it is so thin. Holding it between you and a light source, many small holes are noticed at the intersections of creases and the entire blanket is translucent to begin with, this coupled with the many creases that are in it when you purchase it takes away a significant amount of it reflectivity. It is very easily creased as well which also detracts from its ability to reflect light. And while it is reflects nearly 90% of radiant heat energy, it is only able to reflect around 70% of the light.
The largest advantage of using this type of material is that it is very cheap and therefore easily replaced. Emergency blankets can create hotspots if not attached flush to the wall so it is important that no air gaps exist between it and your supporting wall. The easiest way to attach this is to use tape (Aluminum or metal tape is recommended), as it tears very easily once it is cut or punctured.
Source:
https://www.420magazine.com/forums/how-to-grow-marijuana/71077-what-reflective-materials-can-i-use-my-grow-room.html
