[Swansea Hackspace] What type of pleat?

[Sharon Mitchell]

That does indeed look like a box pleat.
You can achieve a contrast fabric 'within' the box by sewing in a strip
where you want the pleat before you sew it up - if that makes sense.?

You may also - depending on what fabric you're using - want to use some
interfacing to give some structure and stability to the
garment/shoulder.

You'll then need to find the centre-point of the short-end of this
inserted strip and fold the seam edges into this point and secure, both
ends will give that 'slit' look, whereas most box pleats are
'one-ended' and give that triangle look. (e.g hems on skirts)

I've got some notes here that I'll get to the 'Space for Saturday - the
instructions are for a bag - but just focus on the pleat construction
bit - should be what you need.

N.B: a hot iron (if fabric permits) is your friend when working with
pleats ;)

HTH
Sharon