Using this behind the dry-lining in our very old house. The rooms that we could never get warm and always felt uninviting now warm up quickly and stay warm. Been able to almost turn off the radiators in them as well so definitely saves money in the long run.
This was easy to put up and there does seem to be an onmprovement in the level of insulation which was poor.
Have to wait for next winter to tell for sure.
I purchased the foil to black out windows in our van for overnight sleeping. It does the trick. Added bonus it can be used to keep the van cool in the daytime.