Making and/or owning a Xenomorph costume is a dream for some. As Instructables user Mostlymade put it, “There comes a time in a man’s life when he has to put aside his childhood dream of having an Alien costume and actually decides to do something about it.” He dove into the project figuring that if he could do a good enough job carving the Alien head from foam, he’d think about making the entire costume. As you can see, he succeeded. He’d described the process of creating the Xenomorph in plenty of details (no chest-bursting, thankfully).’

Here’s what he did for the shoulder piece pictured below.

You can see here I glued split foam tubes on as the ribs.

I needed sturdy, lightweight pieces to support the shoulders so I opted for a thin sheet of epifoam which I cut to fit the curve of my shoulders so it sturdy. This was glued on with hot glue.

You can also see here I added chest and shoulder details with pieces of sheet foam which was hot glued on as well.

Once the epifoam was in place I took black foam insulation tubing and glued it along the top curve of the shoulder piece. I tapered the from end to make it look like it slid into the chest, giving it a more accurate and smooth look.
epifoam does not take paint well, so I covered it with black fabric which I hot-glued on. I used a lot of glue along the curved edge because the tube is under pressure from the arc and I wanted to make sure it would stay.
I covered this edge with a quarter piece of ribbed plastic tubing with his the seam and added another layer of detail and tubing to this area which looks great.

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