"As a little tip of the hat to the fans, I wanted to pull off the suitcase suit," he says. "In the comic book, they have this ridiculous thing where Tony Stark would open up an attache case, throw a glove on, and on the next page, he'd have the whole suit on. How do you make the suitcase suit real? That was another challenge we presented to ourselves." - Jon Favreau
The original version of Iron Man was big and bulky. It had a lot of cast iron pieces and it limited the artist. Stan started improving it immediately. In the first issue, Iron Man was iron gray. In the second issue he noticed that people were nervous around him and, at someone's suggestion, he painted the armor gold (earning the nick-name the "Golden Avenger"). That wasn't good enough and a few months later they redesigned the armor completely. Don Heck had been doing the art with Jack Kirby providing some of the breakdowns. For the redesign, Steve Ditko took over the strip for an issue or two.
The new armor was light and flexible. It had the red chest piece (it actually covered his entire torso) which Stark could wear over the unit keeping his heart beating. To put on the rest of the armor, Stark would pull on a red glove or put a foot through a thick red ring. Golden armor would emerge from this, pulled up his arm or leg by magnets and lock into place in the chest plate. The boots worked the same way. He just stepped on the sole and the boot covered his foot. The mask slid over his head like a hood. The faceplate was hinged and could be raised. It also has larger eyeholes so his expression could be seen through it. The whole assembly was so small and light that he could put it in his attache case and carry it with him. The lock could be set to release tear gas if someone unauthorized opened it. This had to be set separately, allowing someone to steal his armor once.
This remained the basic armor well into the 1980s. There were a few modifications. The face plate became part of the helmet. The pods on his hips grew. The position and size of the unibeam and two smaller plugs moved around.
In the late 1970s, the helmet was redesigned to allow for Stark's nose. It looked ridiculous and Stark quickly returned to the original helmet.
He also went through a phase with red and white armor instead of red and gold. Eventually the armor was redesigned to look more armor-like and began looking like the suit(s) in the movie.
There was a long-running debate in the letter column about the armor. It was flexible when it went on and it had no visible joints so how could it give Stark added strength or even protect him from crushing force?
Eventually a writer threw in the word "polarized" and the debate stopped. Apparently the armor stiffened when a current was applied to it. What is more, it would take different shapes depending on the current, allowing movement.
Something that no one ever commented on is the weight. A thin sheet of high-carbon steel can be pierced by bullets and would weigh something in excess of 100 pounds - not something you could lightly carry with you. Stark's armor is significantly stronger than steel and significantly lighter.
Then there are the batteries. Most of his power was supposed to come from the pods at his hips plus (indestructable?) solar cells in his armor. Batteries that size are more suitable for powering a laptop than a battle suit.
But that's comics. A large portion of disbelief is required.