When sewing thick layers, I like to use a mix of techniques and special accessories. For many of the bag patterns for the bags that I’ve made in classes, there is a foam layer used to add body, shape, and padding – the brands we’ve used are Annie’s Soft and Stable (pictured here) or Bosal, which has one side coated with an iron-activated adhesive. These techniques can also be used with different kinds of batting, or multiple layers of fabric of varying weights.
Working with these thick layers can feel like a wrestling match, especially if I’m using my small machine (these photos are taken while using my big machine). Most of the bag patterns call for a 1/4 – inch seam allowance. Because of the thickness, the funky shapes (we’re often sewing pieces that come together as curves or are already curved), and the difficulty of keeping everything matched up, one of my favorite special accessories to use is a 1/4-inch foot with guide. I think quilters are familiar with presser feet called 1/4 inch feet and/or patchwork feet – this is one from Bernina, the #57 foot. With this, as long as your edges are even and trimmed to begin with, you can keep them matched up and pressed right against the guide (needle in the center is the only position allowed with this foot), and it gives you a perfect 1/4-inch seam. Well – usually you still might have slight wiggling, but that part is human-caused!
Additionally, you can see that I’ve also prepared my edges on the individual pieces to be sewn together. What you see in the photos below is a layer of quilting cotton on top of a layer of the stabilizing foam (Annie’s Soft and Stable). What I’ve done here, after using a decorative stitch to quilt the piece, is I’ve neatened up the edges with a straight edged sewing ruler and a rotary cutter, on my cutting mat. Then I used an overlock foot (for Bernina that’s a #2 foot) and the simplest of overlock stitches (for most Bernina models that’s a #3 stitch) to secure the edge of the fabric to the edge of the foam – this also has the effect of compressing the foam a bit at the edge, which ends up making it a bit easier to send two of these through together in the next stage of sewing the bag. If your machine doesn’t have an overlock stitch, a simple zig-zag is the closest similar stitch. Alternately, if you have a separate serger or overlocker machine, those are perfect for this task.
Even though my machine can handle thick layers, having them neatened and slightly compressed has the added benefit of reducing the amount of wrestling required. See the three pics below.