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Why do raw denim jeans withstand hundreds of pounds of tension without splitting, while a luxury silk chiffon gown hides every raw edge inside an invisible, whisper-thin fold?
In fashion engineering, garment durability and finish come down to two precise choices: the stitch class (how threads interloop) and the seam type (how fabric plies are folded and joined).
Stitch Classifications (ISO 4915)
The international standard ISO 4915 categorizes stitches into numeric classes based on thread configuration and loop mechanics.
A lockstitch (Class 300) locks a top needle thread with a bottom bobbin thread in the center of the fabric ply, producing a flat, stable join with zero stretch.
📊Interactive diagram
In contrast, chainstitches (Class 400) and coverstitches (Class 600) form extensible loops underneath the fabric, allowing seams in athletic wear and jersey knits to expand without snapping under tension.
What happens when we arrange the fabric plies themselves before stitching them together?
Seam Classifications (ISO 4916 & British Standards)
Under ISO 4916 and British Standards (BS 3870), seam assemblies fall into distinct categories based on fabric geometry: Superimposed Seams (Class SS), Lapped Seams (Class LS), Bound Seams (Class BS), and Flat Seams (Class FS).
While superimposed configurations overlap plies, Flat Seams (such as a Flatlock Seam) butt raw edges together with zero overlap to minimize chafing, while bound designs encase fabric margins in a Bound Edge.
Under ISO 4916 and equivalent British Standards, seams are categorized by ply configuration: Superimposed Seams (Class SS), Lapped Seams (Class LS), Bound Seams (Class BS), and Flat Seams (Class FS, such as a flatlock seam where raw edges butt together without overlap).