This is the strap I made for this last bag/purse I finished - love the accent along the sides. One other bag I made a while ago I used the same technique and the strap is comfortable and has worn well too. This strap measures about 1 1/2” wide not counting the cording on the outside edges.
I constructed the strap in two long pieces. For the first side I stitched the cording to an interfaced strip of one of the black fabrics and then I pressed the seams to the inside.
I cut a piece of Soft and Stable the length of the strap then seamed a piece of the black fabric around it. I centered the seam on the backside and pressed the seam open. I did make sure I had seamed this fabric tight around the Soft and Stable. I folded the Soft and Stable while stitching the seam on the fabric that worked pretty well. I could have used a more traditional method and turned it inside out and seamed it then threaded the Soft and Stable through but that just sounded like too much work and I think the knit fabrics on the outside might not have slid too well anyway.
The last step was to stitch the strap to the bag. I stitched the padded side to the inside so it would be more cushion for when I carry my camera in the bag or when I carry more weighty items.
On the night I gave the program a fellow quilt guild member asked about and we discussed keeping bag straps from falling off or sliding off your shoulder. We discussed that problem and around and wondered if stitching a small strip of the fabric made for slipper bottoms to the top of the strap would be the solution. What do you think? Do you have any other ideas?