A chenille machine uses a hooked needle to pull yarn up through felt. Sewn as a loop stitch, often called moss stitch, it leaves a raised pile that gives varsity letters their soft texture. Sewn as a chain stitch, the same yarn lies flat in a linked line that is used for outlines, lettering and detail.
A chenille file is planned around those two stitches. The digitizer decides which areas are moss and which are chain, the direction and spacing of the fill so the pile looks even, and the order the areas sew in so the felt stays flat.
Manufacturers describe the same split: Tajima's TCMX chenille series sews "loop and chain stitches", and Barudan America's chenille machines switch between loop and chain at high speed (both pages checked 17 September 2026).
Chenille is not something a flat embroidery file can imitate. If you only have a standard embroidery machine, ask about a flat or appliqué version of the letter instead.