This weekend I'm sewing a couple more grocery bags. They are easy to make, sew up quickly and are very useful. It is also nice to make something using only the most basic sewing ingredients--thread and fabric.
Since they need to be durable, I've been using a double seam. The double seam is just like it sounds--two seams.
In this picture below, the seam on the left is the original seam and then a second seam has been sewn 1/8" to the right:
If the first seam comes undone, the second seam provides back-up. The double seam also helps distribute the stress on the fabric.
When I make a hand bag or clutch, I always double stitch the lining. For the grocery bags, I want them to be really strong, so I'm double stitching the side and bottom seams of both the focus fabric & lining fabric shells.
When using a double stitch, you won't be able to press the seam open flat, but can still press it to one side. On bags the top side seams can get really bulky, especially if there are multiple layers of fabric, interfacing and interlining (invisible lining). My preference is to press the seams flat at the top sides whenever possible.
To be able to continue pressing the top side seams flat, I'll start & end the double stitch about 1.5" from the top edge. Then I can still trim any extra interlining (invisible lining) back close to the seam, and press the seam open flat at the top.
