In architecture, filets are used to cover gaps, to bridge shaped mouldings or to provide decorative bordering. They may be plain or as decorative as best fits the purpose.
In soft furnishings we use filets as:
a) several narrow strips stitched together to make a wider piece.
b) a thin strip inset into a piece for decoration or to mask a join.
d) a thin strip cut and added in for a specific purpose, such as a placket or gusset, or tie.
f) strips of wood, metal, fabric or braid that follow and cover the raw edges of fabric walling