I have flat slab garage door that I want to insulate. I saw many videos online and they suggest using garage door insulation kits. However in all the videos I saw the garage doors has the groove that can hold/support the insulating sheet.
The problem I have is that my garage door is old flat/slab style which does not have groove that runs along the hinges horizontally.
Any suggestions on what I can use to insulate the door and how?