I am planning out how to sew a pair of rip-away insulated shorts. Sorry this post is long, the main question about seams for joining insulated panels is towards the end.
Insulated shorts you say?? I think of warm shorts as being the equivalent of a vest but for your pelvis. My bottom layers are not easily changeable, so there is always a compromise. These shorts would be light/packable and be something that I could put on over whatever I am wearing. I also think they would add a good bit of warmth for sleeping.
Anyway on to the basic design-
I have drafted a pattern and have made a few test pairs out of old sheets. The shorts are going to overlap on the outer side seams of each leg and have snaps down the side for the closure, hence the “rip-away”. The waist is a curved yoga waistband made of spandex with nylon panels on the sides, where the snaps go. The insulation will be 2.5 oz apex I think (I have samples coming).
An additional design component is that I do not want insulation between my legs, so rather than having 4 panels as most pants are made (front and back for both the left and right), they are made of 6 panels. The additional 2 panels of fabric are between my legs, similar to a gusseted crotch, but they go all the way to the bottom hem of the shorts.
It is these additional panels that are causing the most difficulty. I know that the simplest way to make insulated pants is to make an inner and outer pant, and join the inner/outer at the waist and hem. The left and right are then each joined with a simple seam, and the raw edges are inside. This would be the most straightforward way to construct the shorts, but it is not necessary to have a double layer of fabric in the inner leg. I plan to use some softshell fabric for the inner leg panels, and doubling the thickness would add an additional 1/2 ounce, so I would rather leave it as a single panel.
So, given that I want a single layer of fabric in the inner thigh, the next obvious way is to construct the left and right legs separately, and then join them together with the crotch seam. So this crotch seam would go down from the waist with the L/R insulated panels, through the crotch with the single layer softshell panels, and up the backside with the L/R insulated panels again. I intend to have the raw edge of the softshell panel encased between the shell/lining layers as well. The topology and order of construction is kind of complicated to think about, but it is this seam that I don’t know how to sew. It should be flat and not bulky and enclose the raw edges of the left and right halves.
A french seam in the crotch seems like it would leave too much of a ridge. Would a flat felled or mock flat felled seam work to join the two insulated panels without being too bulky? I think the flat felled seam would result in 4 layers of insulation, 4 layers of shell, and 4 layers of lining. Is there some other way to construct the shorts that I am not thinking of, while keeping my requirements?
Perhaps I am overthinking this, but these are going to be haute couture insulated shorts! I can’t have unprofessional raw edges exposed :)
Thank you!
