Is this door made of metal and comprised of several hinged panels?
If so, I have insulated some of them in the past by purchasing rigid, 4' X 8' sheets of either plain styrofoam insulation panels, or the same size urethane insulation panels and cutting them into sections (batts) that will fit into the spaces of the door interior panel "voids".
I used 100% silicone caulking to seal the styrofoam batts to the door panels (last step). Most of the door panels I worked with had an angle lip (stiffening structure) that ran all the way around the interior edge of each door panel.
To get a good tight fit of the styrofoam sections to the door panel voids requires cutting the styrofoam panel into two pieces lengthwise which can be inserted one at a time into the void. Insert each section into the void edge lip first, then press the centers of the sections together for a tight fit.
I then used 1/4" wooden "lath" strips, cut to fit between the upper and lower lips of each door panel to hold the styrofoam batts from falling out. Some door panel voids were deep enough to allow 2 layers of 3/4" thick styrofoam batts.
After getting the batts in place and secured with lath strips, I sealed the edges of the batts to the door panels.
After completing the job on a couple of doors, I had to add some tension to the springs that assist lifting the door when opening. That was simply a matter of cranking down on the tensing eyebolts that the springs attached to.
The doors were all "manual operating". If a door opener is present nothing needs be done to compensate for added mass to the door.

Thanks for the info. My door is wood, but your info gives me some good ideas.
When i built this addition, onto my house, i found a very good commercial wood door, along with the over-head roller type of lifting spring, but i installed the side springs instead, as i didn't have room for the big spring above it. The door had anti-theft protection wired onto it, so that came off, and plywood covers on each panel, too.
Right now, i can unlock that 12 ft. wide by 10 ft. high door and lift it with one hand! But, the springs are stretched as much as possible, as i ran out of room for more expansion. The added weight of the styrofoam might make it too heavy. So, i'll have to keep it as-is. Thanks for the reply.
P.S.: There is no room for an electric opener. I made the ceiling higher, so i could work on trucks and vans, and not have to duck my head, as i am 6'2! And, the lower floor negates gasoline fumes from seeping into the main cellar, and away from the furnace.

The door springs would never know that you added styrofoam. You could also wire a few windings together so they can't expand. That would effectively give a little more strength.

I hope you have a cable going down the center of the spring in case it lets loose.

Also, springs can be bought that will lift more weight with the same length. And are all the rollers lubricated?

Rusty , just a further point of info to add to both Mownies and Bays excellent points of info . You may wish to consider "Roxal Semi Ridgid" Insulation for your selection . It is excellent form of R Factor used commercially for yrs and within the last few years being applied within domestic use. It also has great noise attenuation characteristic's and will not absorb more than 2% its weight of moisture and if it does it will wick out the moisture in short matter of time . It is a man-made Mineral Wool form of Insulation which is also Fire Proof. I have applied it for my Diesel Generator Room for Noise Reduction Properties with Contact cement on the backing board or Chicken Wire for the Bat Style . Just a Thought Bro !

To: Baymee: Yes, i do have that safety cable in the springs.
I got into installing garage doors at one place where i worked. An irate customer backed his car into one of the overhead doors, and since the boss was "tight" and i had watched a door being installed, some time before that, i volunteered for the job.
Really, they aren't all that tough to do. And thats why i did my own door. I bought the door in "used-as is" condition, for $75, and did the job. I had to install a "low-overhead" kit on the top rollers, but it does work.
I'll wait for better, warmer, weather to put insulation on it. Thanks for the help!
Rustyj
P.S. As for oiling the rollers--i did that, and they got all gummed up, so i squirted some mineral spirits into them, and they loosened up, and i can lift it with one hand again. I had been told not to oil the rollers, so i guess that person knew what he was talking about.