In this section we're going to cut the insulation to shape and sew its darts closed by hand. At the end, we'll also finish up with the shell nylon, which is just a few easy steps.

Approximate time: 1 hour

Lay out your insulation one layer on top of the other and lined up. Handle the 3D carefully. It's extremely grippy, so work on a slippery surface like a tile floor or large board if you can because it really hangs onto carpet. Be very sure that you're not stretching it out. It's easy for an edge to grab and put tension on the whole thing, which will severely reduce the loft. After you lay out and line up both pieces, fluff them from the edges several times and let the whole thing sit for a while to make sure that it's lofting properly.

Get your shell. You'll use it as a template. Lay it out on top of the insulation. If you lay it wrong side up, that will leave the insulation oriented so that you won't have to flip it when it's time to put the whole thing together.

Cut the whole thing with at least an inch of extra material on the whole perimeter, including in the darts. You'll really appreciate a good pair of scissors here. Put the shell aside again.

Now sew the insulation darts together. I find it helpful to put a can under each one to help it with it's final shape. Again, be sure you're fluffing it as you go and that the can isn't stretching the material. You're going to sew these pieces pretty loosely. You don't want to compress the insulation, just hold it together. I use a doubled up thread on a hand needle. Put the first stitch through then pull it back through the loop in the thread to lock the end.

I use a white upholstery thread from Guterman for the insulation. It's stronger than regular thread, which I think will help on these loose stitches and the white won't show through if a light colored shell or liner is used.

Use a stitch about a half inch from the seam and space your stitches about an inch apart. Keep the needle pushing into the same side each time and pulling the thread over on each stitch. Keep tension on the thread. You can compress the insulation a little, but not super tight. Sew from the center of the insulation out towards the edge and stop about an inch and half from the edge. You're going to trim the insulation at the end and you don't want to cut your stitches.

That's it for the insulation. The last step here isn't pictured, but involves the liner. Sew the darts closed with the seam facing the wrong side (opposite of your X). Then hem the foot end about an inch with the hem facing the wrong side also.