Felled seams are sturdy and utilitarian. We’re mostly familiar with them as the re-inforced seams on our jeans, but felling is a very old technique. It was a handworked finish for seams centuries before sewing machines were invented, and was often seen in traditionally home-made items like shirts and chemises. A seam allowance can be felled after the fact. It’s a good finish for both hand and machine sewn seams, and, properly done, is completely invisible from the outside of the garment.
Please note: You don’t have to trim this seam allowance back quite this far. I have a slightly springy wool that frays like the dickens here, and I’m putting it onto a doll so I want to get as much bulk out as possible. I’ve trimmed both seam allowances so that they will kiss inside the seam, rather than overlapping.
The last two photos haven’t been doctored – the color-shift was caused by me turning on the Ottlite. :)