I had a 300 foot roll of aluminium film in my shed from my last move. Lost track of it, and it wasnt gonna go in my kitchen after i found a dead rat curled up next to it. Besides, the total aluminium used for the job was perhaps 1 kilo, maybe a hair more. Mylar costs lots more than that. i would need at least 2 emergency blankets worth to do the job and thats pushin $15 Mylar is metalicized plastic, which is un-recycleable. while my aluminium will readily get recycled though my local waste management company.
if i wasnt doin all this with scavenged parts, and shit i already had, i might have gone the mylar route, but adhering it to the wall with paint worked so well i may just stick with that for a while.