These parts are the side straps under the armpit that joins the chest to the shoulder blades behind you to stop things flapping around. 

So I started by making a template from many photos of the movie suit superimposed with photos of other peoples attempt at this part until I was satisfied that I had an accurate image. I actually made a pair from foam to test for size and to wear to an event, so I knew I was on the right track. So first I traced them on to some thin MDF

Then I trimmed out the two shapes with a jig saw

Sanded the edges smooth

Then I trimmed my template down to get the thicker inner part and repeated the process

I used a wood chisel to carve the grooves

Glued them to the backing plates

Boxed them up for moulding

Poured a silicone mould

Removed the silicone negative

I brushed the silicone negative with petroleum jelly as a release agent then poured a silicone positive.

Then I made a plaster negative from the silicone positive and poured black tinted latex in to it

Then I trimmed them out and masked off the end flaps as they need the adhesive applied to them. I then painted them with black Plasti-Dip

Then I stitched some denim to the back of my velcro patches, trimmed them out so no denim was visible

Then using some thickened latex I “glued” the velcro patches down. I then glued some velcro to the inside of the chest pieces where these parts will mate and I used super glue to glue the other ends of these straps to the inside of the shoulder blades. They work perfectly!

I used clothes pegs to hold the side straps on to the bottom corners of the shoulder blades until the thickened liquid latex dries and bonds them to the torso.