Engineer's skin...is a suit...???

The different attire I believe is another (misguided) attempt to convey progression of time. Just like the saucer craft for the past and the juggernaut craft in the future.

There are so many other plot details needing clarity, that these issues received a disproportionate amount of attention.

The biomechanoid 'skin' was another ploy to titillate us fanboys foaming at the mouth in anticipation of some connection to Alien. Ditto the stupid Deacon. Alas we were scammed.

I agree the Engineer later looked different from the beings in the prologue. They do not look like meer suits and their heads look sort of artificial too imo.

Possible....

However i think its a case of a Advanced Suit, and i have covered my interpretations a number of times and it would be like when we look at say Snakeskin, Crocodile Skin as far as clothing made from those materials.

We would wear a Snake/Crocodile Skin Pants and Coat but its still a item of clothing... the same with Fur Coats etc.

Well imagine if we had a Technology where when we where these items of clothing they bond with our skin and so we are wearing the Snakeskin just as it would be on the Snake etc.

So the Engineers Suit is basically a Advanced Version of this

That is somewhat Organic and Bonds with the Engineer, and even integrates some Advanced Life Support Functions that maybe allow them to filter hostile chemicals on the surface of LV-223  And also allow them to be connected to the Cryo-sleep Pods..

And also to connect to the Space Jockey suits and Pilot Chair.

So its kind of like a Biological version of this

My first impressions of seeing the Engineer in his suit was that he was either 1. a cyborg;  or 2. a crazy xeno-human hybrid.  After watching Prometheus, I have to agree with BigDave that it is a suit, but it is somehow bonded to the Engineer.  If you look at the forearms and the neck area closely, the texture of the "skin" is different from the thicker body armor of the rest of the "suit."  These would seem to be the areas of the body where the suit ends and the Engineer's natural body are fully exposed.  The hands and head look fairly normal in an extremely pale person sort of way.  I suspect that the Engineer had to undergo some sort of procedure to allow his body to bond with the suit and that it isn't all that easy to take off.

I believe it is a suit as well. Blomkamp's concept art shows Ripley in the Engineer-type suit. I know this isn't canon (yet?) but it can give you an idea of the concepts adopted by the director. 

I also think it is a suit that bonds to the body. Similair to the SJ suit that bonds to the SJ chair so it looks like it's grown out of the chair. In Prometheus you actually see this when the engineer enters the chair and suit.

The thing that gets me is that you see the suits lined up in the entryway to the flight control chamber, (you also see the suits in the trailer, in the scene were someone says "what the hell happened here?".) These suits have the elephantine nose thing that sticks out the bottom, like the original.

But, when the engineer gets into the chair to start up the juggernaut, he is wearing no suit, and the built in helmet that's already attached to the chair lowers and wraps around his head.  Why do they have the suits in the hallway? Its as they intended to have the engineer don the suit than sit in the chair, which would then mold and connect all around him, with an end result looking like the original space jockey.  But then went another direction and just attached the helmet to the chair itself and gave the engineer a built in skin that looked like the suit in the hallway.....

On one hand we have the separate suits in the hallway, and on the other we have the engineer bio suit and separate helmet combo.....

Skrapha,

There was talk in another thread that the LV-223 Installation didn't originally belong to that caste.  It could have belonged to another that doesn't have the skin suit, thus them needing the flight suits to breathe.

Also if you look the Engineer in the picture is breathing the air that is on LV-223 without a mask.

My theory is that the suit is armour grafted into the body, 'grown' if you like, because that is the most economical, natural way to do it.

why do you need armour? Well, if alien original sin is anything to go by, the engineers are dying and use the xeno dna to try and make new lifeforms that can extend their life, this involves 'harvesting' human planets after being bombed. Wouldnt you need armour if xenos were running around, or you were handling them?

the engineers in the juggernaut look like they are specifically designed for warfare or handling dangerous environments.

@Skrapha

If You look at the scene where the engineer mounts the chair the ribs of the "suit" comes up from within.

 @Necronom IV 

Sorry, I did'nt see Your post before posting.

could be that the elders are like peter weyland (alive) and younger ones especially later on are like david 8, walter, ash, bishop, call and so forth (androids). then with the help of advancement, most presumably the black goo you will see how different things can merge and mutate. all open to debate :-) i posted a while ago several posts about the engineers being bio-mechanoids like HR GIGER always wished inside the franchise, that the alien is the perfect end result of all those different elements (engineers, humans, androids + black goo = woopie doo an alien - perfection)