Kirk,
This is a real common issue for guys building home recording studios... albeit the question is usually in regards to sound proofing, but thermal issues are also necessary to deal with.
I'm sure a lot of folks use the typical blue styrofoam and try to snug fit the stuff in the panels. The only problem is that because the styrofoam is non-porous, and a low R value (R-3 to R5/sheet) it has a real tendency to sweat on the metal door... eventually rusting it.
One of the typical insulating materials I see used a lot for metal garage doors, is mineral wool. It's typically used to insulate in super hot conditions... like around furnaces and steam pipes. So, it can easily handle a sun baked garage door.
By using mineral wool, or it's somewhat more expensive cousin, Owen-Corning 703 (rigid fiberglass panels), you'll get an added benefit of increased sound isolation. This will go both ways... sound getting out and sound getting in. It won't be sound proof, but there will be a significant reduction in that metal door sound.
You can get mineral wool and OC-703 several different thicknesses; 1", 2" 3" etc., and the size is usually 2'x4'.
It's not light though. Both products weigh in at about 3lbs/cu ft. So, you may want to calculate the weight you'll be adding to the door, and verify that it can be re-tensioned to still work. (It's not always a problem, but better to be safe than sad and mad, right?)
Cut it to a snug fit in the panels.
Some folks wrap burlap or other cheap breathable material around the face and edges of the mineral wool. Since your door will be opening as a functional door, you want to do this to trap the mineral wool fibers, and keep them from flying around.
If nothing else, I'd wrap the ends with material to keep the fibers from flying around. Then put something like a 1/4" luan over the top of that, and screw the luan to the edges of the door panels. You'll wanna' leave a bit of a gap between the panels, and/or cut the luan on something like a 30-45 angle so it doesn't bind when you open the door.
Mineral wool is made from slag in the metal smelting process, so it's actually pretty heavy in the itch factor. As much of the stuff I used here, I really recommend long sleeves, gloves, a dust mask and safety goggles.
It easily cuts with a box knife and because it's semi-rigid, it'll slide right in the door panels and sit there.
The best part of using mineral wool is the cost. This stuff is dirt cheap. I got mine from
http://www.spi-co.com/
I got my stock from Reid in the Greensboro office... Great guy to work with.
Raleigh, NC
1513 Sunrise Avenue
Raleigh, North Carolina 27608
919-828-7102
919-828-1633 FAX
raleigh@spi-co.com
Charlotte, NC
Woodland III
3300-A Woodpark Blvd.
Charlotte, North Carolina 28206
704-598-9899
704-921-2950 FAX
charlotte@spi-co.com
Midland, NC -- Presnell Insulation
4297 Hwy. 24/27 East
P.O. Box 169
Midland, North Carolina 28107
704-888-4937
704-888-1312 FAX
800-438-5126
midland@spi-co.com
Wilmington, NC
216 Old Dairy Road
P.O. Box 10538 (28404-0538 )
Wilmington, North Carolina 28405
910-799-8444
910-799-8509 FAX
wilmington@spi-co.com
Greensboro, NC
207-A Creek Ridge Road
Greensboro, North Carolina 27406
336-691-0008
336-691-0010 FAX
greensboro@spi-co.com
