Question: what are flat felled seams?
Answer: Felled seam, or flat-fell seam, is a seam made by placing one edge inside a folded edge of fabric, then stitching the fold down. The fold encases the raw edges protects them from fraying. ... The flat-felled seam is the type of seam used in making denim jeans, although it appears inside-out to reduce stitching.