Foil is a film applied with a die and heat; it sits on the surface and can be very reflective. Metallic ink is ink (often Pantone metallic or similar) printed like any other color. Foil has higher contrast and "pop"; metallic ink is simpler and often cheaper for large or gradient areas.
Foil
Foil requires a die and a separate stamping pass. Best for discrete areas, logos, type. High reflectivity and sharp edges. Cost is driven by die and sheet count. Not suitable for full coverage or soft gradients.
Metallic ink
Metallic ink runs on the press with other colors. Good for large areas, gradients, or when you want a metallic look without a separate pass. Softer sheen than foil; no die cost. Some substrates and finishes affect how metallic ink looks.
Choosing
• Discrete accent, high shine: foil.
• Large area, gradient, or lower budget: metallic ink.
• Ask the printer what they offer and the cost difference.
Common mistake
Expecting metallic ink to look like foil. Metallic ink is subtler. For maximum impact in a small area, foil is the right choice; for coverage, metallic ink may be sufficient.