Last Fall I did the routine weatherstripping around my 3 steel entry doors, including new sweeps. No air infiltration this past Winter, but I was puzzled by how cold the inside surface of the doors felt. Metal is cold, but these doors get much colder as the ouside temp drops. If there is insulation inside, then the warmth inside should be keeping the doors at a somewhat constant temp. So, I'm thinking that either the insulation inside the doors has broken down, or else there wasn't very much in there to begin with. These doors are 20 years old, so perhaps they didn't care about stuff like this back in the days of cheap oil. Tapping on the doors gives what seems like a hollow sound, but I can't be sure about that. I was thinking about possibly trying to fill the inside with some low expanding foam via small holes drilled into the sides, and then sealing the holes. I don't have a problem trying this on one of the doors, but first wanted to find out if anyone else has done this, or has knowledge of how steel entry doors were insulated 20 years ago. Thanks.