Flap Steak vs Inside Skirt — What's the Difference?
Quick Answer
Flap Steak (flap steak (sirloin flap)) and Inside Skirt (inside skirt steak) are not the same cut: Flap Steak is sirloin primal (Bottom sirloin, obliquus internus abdominis muscle); Inside Skirt is plate primal (Transversus abdominis muscle — the inner diaphragm muscle).
Canonical entities: Flap Steak · Inside Skirt
Side-by-side
| flap steak | inside skirt | |
|---|---|---|
| Primal | sirloin | plate |
| Muscle / location | Bottom sirloin, obliquus internus abdominis muscle | Transversus abdominis muscle — the inner diaphragm muscle |
| Character | A thin, coarse-grained steak from the bottom sirloin. The American name for what the French call bavette d'aloyau. Open grain absorbs marinades extremely well. Popular for fajitas, stir-fry, and carne asada. Often confused with skirt steak but from a different location entirely. | The 'other' skirt steak. Thinner, wider, and slightly tougher than the outside skirt (which is the standard 'skirt steak'). Most restaurant fajitas use inside skirt because the outside skirt is exported or sold at premium. Requires high heat, fast cooking, and slicing against the grain. |
Key differences
- Different primals: sirloin vs plate.
- Texture and slicing: compare fibrous, grain-heavy cuts vs more tender steak-style muscles based on each cut’s description.
- Retail naming diverges by country—always map through a canonical cut when translating menus or labels.
When to use each
Flap Steak
Pick Flap Steak when you want its specific marbling/texture profile: A thin, coarse-grained steak from the bottom sirloin. The American name for what the French call bavette d'aloyau. Open grain absorbs marinades extremely well. Popular for fajitas, stir-fry, and carne asada. Often confused with skirt steak but from a different location entirely.
Inside Skirt
Pick Inside Skirt when its primal/muscle traits fit the dish: The 'other' skirt steak. Thinner, wider, and slightly tougher than the outside skirt (which is the standard 'skirt steak'). Most restaurant fajitas use inside skirt because the outside skirt is exported or sold at premium. Requires high heat, fast cooking, and slicing against the grain.
Flap Steak and Inside Skirt are different canonical muscles/primals: Flap Steak is sirloin (Bottom sirloin, obliquus internus abdominis muscle); Inside Skirt is plate (Transversus abdominis muscle — the inner diaphragm muscle).
Choose based on tenderness, marbling, grain direction, and how you plan to cook (sear vs braise vs slice thin).
Read the full guides: flap steak (what-is) · inside skirt (what-is) · flap steak hub · inside skirt hub