I have a three car garage with three separate garage doors (one 1.5x wide in front, one 1x wide in back, and one 2x wide in back). While I do not intend to make the garage a conditioned space, I did want to control the temperatures somewhat, since the temperature differential can be felt through the floor of the rooms above.

Initially, I purchased and installed Reach Barrier 3009 kits on each of the garage doors. While this took the edge off of the max garage temps (peaks around 85F, when it's 105F outside), I figured there was still quite a bit of improvement to be had. Since I really only considered getting garage door insulation products on Amazon, I quickly narrowed my search down to the Owens Corning 500824 kit, and a bunch of R-4'ish foam board products. While the 500824 costs more, it is still much cheaper than buying an insulated garage door.

I purchased 4 kits for my doors. Each kit consists of four, 2 sheet bundles, wrapped in clear plastic. This packaging method is less than ideal because it leaves wrinkles and some delamination on some of the edges of the vinyl. Fortunately, that wasn't a big deal because I managed to trim most of the imperfections off when cutting the panels to size. If you need to use more of the sheet, YMMV. I was pretty precise with my first couple panels, but determined that it was probably best to actually have them oversized by about 1/4" in each dimension as I went on. Cutting the sheets is a little bit of a pain, because of their thickness. I used a long straight edge and a box cutter, though there may be better ways to do it. I compressed the sheet on the facing, and cut along the straight edge to get a clean cut on both the facing and through the fiberglass. I recommend using a clean blade, since it gets messy if you snag the fiberglass. The kit includes gloves, and it's always a good idea to have long sleeves on when working with fiberglass. Depending on where you're cutting it, it's probably not a bad idea to have a mask or eye protection on, either.

The clips look pretty flimsy, but work fine in practice. I found what worked best for me was to clean the door surface, and apply the adhesive pad. If the door section didn't have the lock bar across it, it was best to put the door clips on first; while it was best to get the insulation sheet in place first if there was a bar. I used the box cutter to cut the square for the door clip with the sheet already in place. The 1x door took me about 50 minutes. With the learning curve out of the way, I found that the 2x door took about the same amount of time.

In an unlikely coincidence, Houston had uncharacteristically low temperatures (~20F) right after I installed the kits. The garage stayed in the 55-60F range, when it would normally be around 40-50F. I'm excited to see the results in the summer when I've also added new door seals and weatherstripping!

This was the highest insulation rating I could find for garage doors. My door's sections did not have edges to tuck the panel in on both sides. The left side had nothing to hold the panel in, so I made some small metal pieces to put in the center of the left side and adhered them using 3M double sided tape. The door gets hot here in the Summer so duct tape comes off and leaves that sticky, gooey glue (yuk). The panels on my double garage door added more weight than I expected, so now the door is much harder to lift, whereas it was perfectly balanced by the springs so it would life easily and not move up or down when the door was half way open. Now I have to twist the springs a 1/2 turn or so to add more force so the door will be balanced. My garage door opener is able to open it still, but it is working pretty hard and will probably malfunction unless I twist the springs more. It is not so easy to open now. The clips are okay and seem to hold the panel in. I used some scrap pieces to go around the windows at the top of the doors, but may just cover the windows with panels, since the windows get very hot in Summer and transfer the heat into the garage. I could just put sunscreens on the outside of the windows and that may cut down the heat transfer.

Instillation of both kits went smoothly with two of us working together, and like everyone says, it took about an hour. It was obvious right away that the clips alone were not going to hold the insulation snugly in the door. One roll of white Gorilla Tape was sufficient to hold one kit. The taping added another hour to the whole process. The weight added to the door did slow the door marginally but not enough to stress the motor. Garage is much quieter and cleaner looking.

The shipping label was placed right over the instructions which are on the outside of the box. It comes with "clips" so I have no idea how they go on the door. You must cut each piece to fit the standard panel so you have waste sitting around. I foil taped them to each section so it worked out ok.
And yes I was stupid and didn't read and thought it did a whole door. As one can see Mr. Pink panther has a car parked in front of the other section so yea ordered another one. Was going to just go with a standard roll but could not find any that was not wall thickness. Yes we have city codes for inclosing a garage soooo I just left the door up. Call it the flapper and the design is at the Patten office. Haaaa

Not the best option for insulating a garage door. Only (2) clips to hold up a 2' x 4' fiberglass panel. Photo is worth a thousand words! Sorry, photo came out sideways.
Lowe's has solid panels that are my next option.