I was thinking about insulating my garage door for quite a time since living with the summer heat in North Texas. So I did what yall did and look around if anyone sold garage door insulation kits. I did see one at the home depot, but paying $49.99 for a kit that only did a 8' door and having to buy 2 kits to do the entire door costing $100 bucks.. So I thought and looked by the home insulation section to see if there was any cheaper alterntive to having the same protection. I came across some packaged foam that was a 1'X 3' sheet which came in 6 sheets in a package. So I guessed and got 4 packages of the foam which was pretty cheep. I also looked at the 1/4in X 4'X 8' sheets of insulation that was silver shiny on both sides and had foam in the center, so I grabbed 3 sheets. The last thing I looked for was aluminum tape to tape in the cracks of were the insulation was placed in.. All of the supply's cost around $50 bucks.
When I got home I started working on my project. I installed and used the white foam first, and used a little aluminum tape to keep it in it's place. After installing the foam, I got my stright edge, measured and cut out the correct size for each section and placed it behind the white foam.
Last I used the aluminum tape to seal the edges around the insulation to keep what was left of any heat to seap through. And ya know, it worked just as good "if not better" than buying the kit and costing half as much.
So if your a do-it-yourself and don't mind spending half a day and half the money to install your own garage door insulation kit, then go for it!